This one is a common issue, so it is best to be prepared. By and large, delays are understandably hard to avoid (such as unforeseen traffic issues) and are forgiven by guests who came on time. That being said, here are a few things you can do to do your best to keep it from happening:   Ensure that invitations are clear as to the time of the event and if requesting an RSVP, ensure that the time is confirmed. Communicate with (via your contact sheet) the MC, relevant guests (often the leaders of the party members), entertainers and kitchen staff as soon as you're aware of an issue you cannot resolve easily.  Should the delayed guests be the focus (such as the bride and groom), the usual methods are: Contact the delayed guest/s directly to check for an estimation. Advise the kitchen immediately of all developments so they can slow down or speed up to keep time. Refrain from making it known publicly that the event is being delayed because of certain guests (because the party will work that out on their own), but advise key hosts or members of the party that you have been made aware of the fact. Let them know what you intend to do, but allow the hosts to make a suggestion as they know the members of their party and what would be appropriate in the context. Maintain careful watch on the time in relation to speeches. If key guests are late, serve an additional appetizer (first course) and/or beverage early as this will prevent guests who came on time from becoming bored and will keep them occupied. For guests that are going to be delayed for more than is reasonable or possible (such as when serving food that simply cannot wait, such as souffles), start the event as planned and when the delayed guests arrive, start them at the next course of a meal (even if this is dessert). Organise an additional dance, game, speech or other form of entertainment (especially music), and ensure extra distractions, such as group or party photographs are done until they arrive and this back-up strategy should be considered the day in advance. For guests deliberately arriving late, it should be seen as that guest's choice, not your fault as manager, so your duty is first to the guests that are already present and to ensure they're looked after. In a nutshell, act as if there is no problem and carry on regardless. This one is rare if you have planned things carefully, however accidents do happen (such as a guest or young child making a mess of a food table, or an accident in the kitchen). Early on you should be aware of the type of guests so you can take into account when and where food is displayed (such as for a buffet) and where such guests are seated.   Any spillage for safety reasons must be cleaned up immediately, even if it means removing a red carpet or desired décor and furniture to be able to do so. If it is impossible to hide a stain without affecting the appearance or the integrity of the item (such as an antique), then removal is wise. If you have a spare, then use that; if not, move the existing furniture or décor subtly so it does not feel missing. A soft rope barrier, curtain or screen is recommended whenever you need to hide the food area (such as a buffet with chafing dishes, or when organising a "reveal" of the next course), as certain guests may feel that if food is in the dining area, it is free-for-all, when they want -- which is not always the case. Shuffle the menu. If part of a dish is not possible to include (such as a side dish that was burnt), either exclude it altogether, find an alternative, reduce the portion sizes to stretch foods, but increase portions of other foods to balance. Advise table hosts as required. Unexpected vegetarians, teetotallers, those with food allergies, religious or special diets –– no surprise should ever occur with proper planning –– but guests occasionally do bring along additional family members, partners or close friends without advising you, especially if it's not a strict invitation-only event. This is usually easily resolved. Keep a headcount as guests arrive and when they arrive at the door, ask if there are any food requirements and advise the kitchen and service staff immediately. For large unexpected groups that are not gatecrashers, send a team member to the kitchen to take stock and, if necessary, drive out to collect more supplies. Kitchens typically over-cater to cover for accidents and more often there are more cancellations than unexpected guests. Limited portions can be stretched when you provide additional fillers, such as bread rolls, salad or vegetable portions, ingredients for which can be quickly sourced from local supermarkets. It's wise to remember that many managers have made serious errors in underestimating the intelligence or forgetting the needs and desires of children at events, as they have the same needs and wants as adults - to have a good time and not be bored. Remember that their parents are also often offended if the event does not cater for their children. In practice, it is best to request an RSVP for every child that may come.   Young children (under 10) are best given food or snacks early as many dinner events have the meals start as late as 8pm, which is far later than most children are used to. Food provided should be fun and healthy but as special as the adult menu as parents appreciate special touches for their children - it makes their job easier so they can have fun as guests in their own right. Over 10's usually are fine to be served adult food and portions, even if they don't eat all of it, but offer the children's menu to them (with their parent's permission) if they don't seem keen on the options. It has also been known for young adults 13-18 to often request the same food as youngsters, such as a hamburger and fries as opposed to more formal restaurant food and it has been a frequently used trick to re-brand the children's menu as an "Alternative Menu" for this age group of guests. It is very wise to play safe and discuss with key guests about your plans to keep the young and old engaged, well in advance of the date. A discrete area should be provided for mothers with young children for their needs such as toilet/bathroom breaks, breastfeeding (etc.), and a place for very young children to sleep in if they are tired. Ideally this would never happen, but it does –– family or corporate events both. Politics and drama often come out at events that, as an outsider, you would not be always aware of. Prepare yourself.   Ask the client or key guests before the event of the likelihood of such issues, or with selected hosting guests if it is not appropriate to discuss these issues with the key guests, so that way you can ensure that people are seated in places that will not cause issue. Enlist service staff or key-guests to act as unofficial monitors, to keep an eye out for issues and to step in when required. Strictly speaking, your duty is to ensure the event is smoothly run, but only where it is appropriate, and to stay out of issues that are a private concern. Therefore, you should be aware of who within the party are the "peacemakers" of the group. As it can be a difficult job to refuse alcohol to an inebriated guest, or to deal with an inebriated guest that inclines towards anger or violence, it is wise to enlist a peacemaker guest and only involve law enforcement when necessary after consulting with the key guests. Even in small events or backyard events when alcohol is often stored in an ice box for guests to serve themselves, it is equally important to be aware. Gatecrashers are difficult. Should it happen, unobtrusively evict them if appropriate - consult your key guests to verify that they're unwelcome. For large scale and rowdy or abusive gatecrashers, your duty is to protect the existing guests where appropriate and to call security or the police if they do not leave after being politely asked to do so by yourself and/or the key guests. Guests often shuffle name cards about at the beginning where they are sitting, so that they end up sitting next to people they want, or at a table they want. It is wise to check with the key guests how far this is permissible according to them. Typically you should have organised table plans in advance and have received approval from the key guests. Should it be that people must be at certain tables, then it is wise to keep people out of the dining room altogether until time. Often the lobby, foyer or bar area serves this purpose and if it is very important due to family issues, it is wise to group people together and move them en masse to the separate tables by each host-guest and service personnel to seat them in their proper order. Sudden, unexpected rain or snow can be common in parts of the world; likewise, a heatwave or a cold front can also can pose a problem. While weather events are not usually an issue if you're indoors, being outside makes things difficult. If bad weather is expected, then consider moving the event location. If the event cannot be relocated or rescheduled, hire a large tent or pavilion (admittedly this can be pricey on short notice). Keeping an eye on weather developments as you go is important; very little can be done to salvage an event affected by weather, so make the best of what you have. Many parts of the world now have insurance policies in the event of severe weather or other problems. If you are in an area which is known for unexpectedly changeable weather, it is recommended to source a quote if there may be a chance the event will have to be re-scheduled as it will at least cover the client the cost of extending hire of equipment, site and service personnel.
Know how to handle late guests and other guest problems. Know how to handle food issues. Know how to deal with children. Know how to deal with rowdy or intoxicated guests, gate-crashers and other guest problems. Know how to handle inclement weather.