It heavily depends on what kind of deck you're playing. If you're playing a deck with no energy acceleration and a lot of special energy, you'll have a very hard time with stall. Also if you're playing a single prize not very heavy hitter deck, you may have a hard time with some of the stall decks (though I had no problem with Wall Stall with QuagNag at Madison, for example; it just depends on the situation.)
Reshizard on the other hand can pretty much hit for 230 in one turn or two at most. As long as you're playing enough field blowers, you're not going to have any problem knocking out whatever they put up there (field blower to deal with the Lucario/Melmetal with frying pan).
Other decks that have some acceleration and play with at least a decent amount of basic energy - Zapdos for example - and can still hit for something can usually beat it eventually, at least with the right techs. If you're hitting a lot of stall, then include those techs. (Mr. Mime is the major one, to prevent Acerola. Let Loose Marshadow and/or Judge to prevent them from winning with Unown HAND and removing key cards from their hands.)
And then just practice - don't quit turn two, even if you don't think you can beat it. Play it a lot. Get used to being very conservative with your resources. Playing against Stall means not putting things on the board until the turn you're ready to use them when possible. Don't let them field blower/crushing hammer/etc. your cards when it's not that card's turn to actually do damage.
And remember - Stall is successful only rarely, and only when circumstances of the meta are very specific. It's there basically to take advantage of people who don't tech for it. When Stall is rare, for the most part you may just accept that you will lose to it and move on. There's always a deck that you'll just not win many games against, no matter what you play. Zapdos might as well close up shop when Weezing comes out. Pikarom has Buzzroc. Lost March has Ultra Malamar. You play what you think will beat most of the decks other people play - the metagame, after all, being half the fun of Pokémon.