Q:

How does one become ranked by ITTF?

I was playing table tennis and met someone who was ranked 250 worldwide by International Table Tennis Federation (ITTF). Unfortunately, I did not have the chance to ask him how he went about doing this. 
How does one get ranked by ITTF?

A:

Players get ranked based on their performance in tournaments. Per the ITTF ranking page, the ranking system as of 2017 (full details here) incorporates:

Wins and losses against ranked players
Adjustment due to relative strength of opponent
Weighting for different events
Bonus points

There are also multiple tiers of competition:

Men
Women
U21 (Men and Women)
U18 (Boys and Girls)
U15 (Boys and Girls)
Doubles
Teams

In this ITTF news release, the ranking system will be revised, effective January 1, 2018. Changes include:

The new ranking is based on the final positions reached at the tournaments only (regardless the relative strength of the opponent
  player).
Only bonus points are awarded (no rating points are given), which are valid for 12 months, except the World Championships.
NO loss of points in case of losing a match.
Ranking Points are fixed according to the point tables using different weightings for different types of events.
Only the best 8 results are considered on a yearly basis (with one continental event included).
Separated ranking lists for each age category (Senior, U-21, Junior, Cadet), taking into consideration only results in the
  respective category.
Special seeding in case of injury and pregnancy

