A good lead guitar player must, and I'll repeat that - MUST - pay attention to the rhythm.
That means knowing the rhythm part intimately yourself, even if you're not the one playing it. Know the guitar chords and the various changes, because ideally, you should be working off of those changes in your solo.
As you'll see in the video, a safe place to end each phrase is to end up on the root note for the chord that is being played... So it becomes important to know your notes, or a least a quick way of finding them. If you need a brush up on your notes, checkout one of my lessons on guitar scales.
If you're really struggling with how to structure a guitar solo, this video should give you a few tips that will help point you on the right path. Another great way of improving your guitar solos is to find some backing tracks that you can practice with. These will really help you improve your solo rhythm, letting you really practice "feeling" the rhythm of the band.
Anyways, let's get down to business - go on and hit play!
How To Structure A Guitar Solo: Some Tips
Watch the lesson on Youtube