I prefer gin, and here is my recipe--
First get nice martini olives from a specialty store (for just DH and I we use lame ones from the Food Lion but for this first attempt, get something nice-- and pepper stuffed ones are yummy. I think Williams Sonoma sells really good ones.)
I make mine in my shaker-- crushed ice, then 2.5 oz gin and about .5 oz dry vermouth (NO MORE, and you can certainly use a little less.) Make sure its dry vermouth, not sweet! Then I put about 2 oz of olive juice in there. I also drop a couple olives that I have broken open into the shaker. Shake it up, and strain into a glass over at LEAST 3 olives. The drink should be cloudy and smell salty...
have fun!
OH-- Tanqueray makes a really good dirty martini. But seagrams is fine, really. Don't even bother with a super high end or boutique gin because the olive juice will overpower the "delicate flavoring" that those gins have-- and I do love high end gin, but its a waste in a dirty martini! HOWEVER-- DO use a good vodka, because you want the nice clean brightness of a good vodka in a martini. Cheaper vodkas (which are fine, say, in long island iced teas or such) give everything a mediciney vibe.