A suicide is a move that I view as the borderline between beginners and intermediate players. It is very versitile, rewarding, and most importantly, fun move that will possibly help you enjoy yo-yoing even more.
There are plenty of reasons that suicides are hard to learn, but here is some information and a tip that will make practicing them more enjoyable.
Keeping the string aligned is a maxim for most all yo-yo tricks that do not involve rejections, magic drops, or the like. (see the picture-in-picture about half-way through)
As a side note, your rhythm or pace will make a difference in the quality and ease of your suicides (especially the double suicide shown first!). Find the speed that is right for you.
Now get moving through the Instructable, watch the video a few times, and practice once you are finished.
And HA! I used a terribly hard-to-do voiceover.
Step 1: Trapeze
C'mon, you should know this.
A real suicide starts here, but there is a little change you can make to this mount to make the trick easier to learn.
That change is to use TWO FINGERS in the loop to start the suicide, like shown at the end of the video.
What this does is expand the loop that you must put your finger in BEFORE it comes around your throwhand. It essentially makes a bigger target for your finger to hit later.