[Pockets]

Might try the rule of "42". On the Turn, mult your "outs" by 4, and your answer will be (about) the right percentage for making your draw. On the River, mult. by 2 and your answer will be (about) right also. Plus or minus a half to one percent won't be too bad.
The important thing to check for, is the pot big enough to call (Pot Odds).
If you ever run into an old guy with a red Baseball cap on, just say Hi! & thanks.