Rum and Coke: Seems best with golden or dark rum rather than white from my experience. 50/50 Coca Cola and rum. Easy as pie.
Screwdriver: Another real easy one. About 50/50 vodka/juice ratio, though you can obviously do it however you want. I mostly use orange juice, though a mixture of that and pineapple or grapefruit is good too.
Just as a general rule, that I've learned from trial and error, rum mixes with soda, vodka mixes with citrusy juice. Vodka and Mountain Dew is every part as bad as it sounds (I don't know, seemed like a good idea at the time). People praise the deliciousness of vodka and Red Bull, but I think it's just two already vile liquids made even worse.
And of course the old trusty malt liquor. Haha, not glamorous, but can you beat 40oz for $2?? Mix it with OJ and you can call it a "Brass Monkey" though I like mine straight, uncut, yo.
Irish Carbomb: Get a shot glass, fill it with 50/50 whiskey and irish cream (whiskey first!). Drop it into a glass with about half a pint of Guinness and chug. For the love of god, don't let it sit for more than a minute because all the ingredients chunk up and get gross. Has a nice caramel aftertaste. The higher the quality of the whiskey, the easier it is to drink, obviously, but in this case more than others it seems...
Wild Turkey whiskey is okay but still has a bite to it. Jameson is best, but expensive if you're buying much of it. If you want to look cool like The Punisher with your bottle of Wild Turkey, wait until you're an old man with no taste buds and drink it right from the bottle, because when you have something that shitty, it just seems like a waste of time to mix it with anything else.
Mojito: Ugh, This is a little more involved than the others and who wants to waste time mixing things when you're trying to get buzzed with your friends? Best to order this at a bar and annoy the people behind you. Anyway... Mix a couple spoonfuls of sugar, mint leaves and half a glass of club soda until the sugar is dissolved. Squirt in a little lime juice and fill the rest of the glass with white rum. Very light and yummy. Freshens your breath too! Supposed to be served over ice.
Margartia: Assuming you're not just mixing up liquor in one of those buckets of margarita mix... It's basically lemon or lime juice, tequila, and Triple Sec. A 1/1/1 ratio of the three is fine if you're dumb or lazy and can't remember complex things, but here's how to make a better jug of it: 1 liter tequila, 1/2 liter triple sec, a can of frozen lemonade, a squirt each of lemon and lime juice (for sourness) and some crushed ice for texture. This isn't really sour enough to warrant putting salt around your glass unless you're just trying to keep with tradition.
I want to mix up a batch of Sangria for a graduation party my parents are throwing for me later this month, so once I do that and have a solid formula down I'll post it up here too!