you don't want it too tight, or there won't be any room for the glue. You don't want it too loose, because glue doesn't fill gaps very well. If the joint is snug enough that you can push it together by hand (not with a mallet), but won't fall apart when you let it go, you're in the right area.
If you are really worried about the joint coming apart, you can always drill across the tenon and pin it with a dowel, but I think that might be overkill.
Thewoodwhisperer.com has a couple of free videos on tenon making, although mostly geared toward the table saw he has some good info.
Take a few snapshots as you work on this project, and post the whole thing when you're done!
All the best