I try to watch as many videos from people here as possible, but sometimes it can be a challenge because there are so many videos to watch. I like a lot of videos, but like Kat said, I don't want to flood people neither, so I mostly try to like videos that I really like. Ones that I think to myself, "this was great, or awesome, I must like it!"
...with that said, now and then I also try to like 1 or 2 videos from my friends here at YTtalk to show support. If I find someone has surpassed themselves, then I'll like the video for that reason to.