I'm about to get downvoted for this, but in dive bars my go to is a gin and ginger. Just because it's always there and it's hard to mess up (even with relatively shitty gin).

If it's a slightly nicer place I usually go for an old fashioned or a margarita (I really love a good jalepeno margarita). Weirdly, I'm a bit of a Moscow Mule snob so I'm careful about where I order those (and get pretty irrationally upset if it doesn't come in the right cup).

Other than that, I'll drink most things and tend to order off a cocktail menu or order straight nicer whiskey. I'd suggest trying different things over time to figure out what you like. Find out who has good happy hours near you with good food and taste some things. Also find out who has decent cheap mocktails and non-alcoholic options. That's a good thing to know that will serve you well through life and it's good to build the habit of occasionally going to a bar type setting and not drinking.

It can also be fun to mix your own. So slowly start stocking a home bar with the basics. It's easy to find recipes online. For most of my home based cocktails I make syrups with tea (I like sweet things). So, for example, make chai tea, add the sugar (the same way you'd make simple syrup), and then add whatever booze you think will go well. You can do this with any tea flavor you want (including floral tisanes like rose and lavender).