Look and feel. Look is self explanitory, and the feel kind of varies. Loose, wispy buds are a good indication of so-so weed. Not all the time, but I'd say 98% of the time, wispy buds are not the most potent.

A nice hard bud, or spongy bud, that bounces back, are a good sign of some good grown weed.

I find smell means nothing at all. I've smelled bud that smelled good, but smoked nasty.

I guess looks can be fooling to, but like before, 98% of the time, if it looks good, it is good.