Step 1: See if someone else has already requested the feature.
Press Ctrl-F (PC) or Cmd-F (Mac) and search the page for keywords relating to the feature you want to request.
Step 2: If you find a similar feature request, vote it up.
If someone else requested the feature, vote their request up. This adds power to the feature request and makes it more likely to get done.
100 separate feature requests for the same feature will get lost and go nowhere. But one feature request with 100 votes, THAT will get noticed.
Step 3: If no one has requested the feature, add it below.
Just post your feature request as a comment. Features with the most "up-votes" are more likely get done.