For the best success, you really do need to match the hatch. Probably the best book on this subject is Ernie Schweibert's, Matching The Hatch. Published back in 1955, you may be lucky enough to find a hard copy in a used book store. I found a paperback copy in pretty good condition for a couple of dollars. The one difference I would suggest contradicting the book you may want to try using a fly one size smaller than the actual bug.
Some guides swear by that one.
Watching the trout wag his tail, tip up and sip in your fly is worth every bit of effort it takes to learn what the bug is. If you tie your own flies, I really suggest thorax-tied flies. They are nearly impossible to purchase, although I hear there are a couple of fly shops in the Denver region that do tie them. Orvis and others tried marketing a fake a while back. Didn't work worth a hoot.