Q:

Regular maintenance to keep the phone running quickly and smoothly

I've noticed that over time my phone has slowed down and feels laggy and less responsive in general. 
In the same way you'd get your car serviced every year, what can you run to keep your phone running nicely?
I've got One Click Lag Fix installed and to give an example, the messaging app seemed very slow to load so I deleted all the threads in there but it's still slow regardless.

A:

Here is some performance tips:

Have plenty of extra space in the internal memory. The phone uses the internal memory to store apks and caches, if you have very little internal memory, it might make it difficult for the phone to find contiguous area large enough to store and load the cache. While flash-based storage are not as badly affected by fragmentation as disk-based storage, there will still be a major performance hit if the apks or cache file is fragmented into 1000 pieces.
You should not need to clear caches. The caches are needed for the best performance of the phone. If you clear caches, and you have performance improvement, that's just because you've made an extra space and that makes it easier for new programs to create and load their caches. While you might be happy with this, it is only a temporary fix until the program rebuilds the cache and it becomes sluggish again. Best way to resolve this situation is to keep an amount of empty space (about 10-30% of the internal memory, the optimal figure depends on the size of your internal memory), do not install too many programs and uninstall programs you do not use; this way you prevent program you do not use to build caches you do not use. Prefer small programs, which generally produces smaller caches.
Avoid App2SD for applications you frequently use, unless you have Class 6 or higher SD card. Put only big applications that you do not use frequently on SD card (e.g. games); homescreen, keyboard, and widgets should be in the internal memory for best performance (Android prevents you from installing them on SD card, but it is not impossible to force move them to SD).
Avoid program that have background services and avoid home screen widgets. While there are valid reasons for programs to spawn background service (e.g. Music Player, IM, etc) and while some home screen widgets are very useful; they can degrade performance if you have too many of them. Background service and Home screen widgets will eat up RAMs that the OS cannot reclaim as easily as sleeping applications. Android usually will reclaim memory from unused applications first, but only in very dire circumstances that it kills background services and home screen. This is not an outright ban on background services and home screen widgets; just to be a bit conservative in the use of widgets since no OS in the world can smoothly run more programs than it was designed to handle.

A:

Keep on top of your apps: deleting the ones you don't use and the ones that are poorly coded resource hogs.
Clear individual apps caches in Settings > Applications > Manage Applications by choosing clear cache.
Reboot your device periodically (I have no evidence to back up that this improves performance but it seems to work for me)

(this answer is a community wiki so feel free to add or amend)

