Have a proper meal before you go out, and alternate your alcoholic drinks with soft ones, as it will take you a little while to realise that you're getting drunk. When you're starting to feel quite merry, then there's usually still some alcohol waiting to be metabolised, so you shouldn't try and drink loads more at this point as you will get drunk.
Some people will make fun of you for drinking alcopops though, as they just look a bit silly and girly. (Although I don't like the taste of beer or wine, so if I can't get spirits that's what I usually have.)