To pick up a straight guy, you need to get his attention first. This works like a litmus paper on acid and water, something to gauge if he can be picked up or he's still a tough one. Make eye contact for three seconds and look away. Check if he glances back. If he did, make sure you don't get that 'dude, I am going to break your leg' look! That is scary... Otherwise, approach him and try to have simple conversation. Don't go as far as 'want to come home with me' lines.
The objective of the conversation is to learn as many things as possible. Like where he hangs out, favorite beer or favorite wrestler. You want to gain his trust and not to immediately rip his clothes off. Bear in mind that most gays that have 'sex' as their primary objective end up in a hospital bed! You don't want that do you?
You have to make sure that you have constant communication. Invite him once in a while for a dinner at your pad 'wink'... and gear up for a sleepless night!