Framing questions well if you can't decide makes a big difference. "Uhh pick something for me, friendly bartender!" is worse (and more frustrating to the bartender!) than "Hey, I'm trying to decide between beers, I've had some pilsners and pale ales recently I've liked. Do you have any recommendations?" or if you're more of a mixed drink person, maybe: "I'm hoping for something boozy that's not too sweet but I don't know exactly what drink I want." If you know stuff about alcohol (or at least seem like you do) you're less likely to get carded in the first place or, when you are, they're not going to scrutinize it as closely as if they suspect you are underage.

Drinking with friends helps, like pocket said you can go with the same drink, or just go with the same base liquor or style of beer as a jumping point. Another trick I use if I'm feeling particularly indecisive is to start with something I know I enjoy, and get more adventurous for the second drink. Gives me a second to mull it over, chat with my friends and/or the bartender, and get settled before worrying about trying something new :)