Here are my tips:
1) Only pick 1 main keyword per video. If it could have two or three keywords, make two or three more different videos.
2) Have about 3 keywords per video total. So like my main keyword could be "ice cream" and my two others could be "yogurt ice cream" or "soft serve ice cream". My only tags would be those 3 keywords. You don't want to confuse youtube.
3) Write a long video description (300-400 words) with your keyword sprinkled in it. If you're going to have affiliate links in the desc, put them under the first paragraph so they're still "above the fold".
4) Make the title about your main keyword. It could simply be your main keyword.
5) Wait. A lot of people say youtube rankings are automatic, but they're not. You can sort of see at first, but I've had videos at the bottom of the first page rise to the top (1st pos) after about a week or so.
Good luck!