To Split or Not to Split
Splitting the check is an easy way just to get any awkwardness out of the way right from the start. But there are occasions when it doesn't really make sense. If you're going out for someone's birthday, you'll likely want to treat that person. If someone doesn't drink (maybe they're pregnant or in recovery or simply don't drink), they shouldn't be expected to chip in for a bottle of wine or pricey cocktails.
There's no shame in asking for separate checks. Your friend may be on a tight budget but still wanted to see everyone, so don't punish them for coming out. If you plan on ordering a salad and a glass of water to keep your costs low, just ask for a separate check before ordering. Otherwise, your silence implies you're on board. A simple "Hey guys, I'm not drinking (or might have to leave early) ... is it cool if I get a separate check?" should do the trick.
Just Split it Evenly
If everyone has agreed to split the bill and you're dining with four friends, expect to fork over one-fifth of the bill (plus tip). You don't need to pay more, nor should you think you deserve to pay less because your chicken was less than your buddy's swordfish. That's not a fight worth pursuing and will only annoy the rest of the group and sully an otherwise fine evening.
If you're out with a big group and you want to split the check, you might have too many credit cards for the server to split. Don't try to persuade them to accept more cards than the stated policy. It's a rule for a reason. And that's why we have Venmo. No one carries cash anymore and even if they did, who wants to make change? What's more, if you're the friend who's graciously put down his card (maybe to get the points, but whatever), you can use Venmo to send payment requests to your friends, which will prevent any awkward reminders days later.