This is kind of banking off of what Jacob said, but I think it's crucial to establish what matters to you. For example, I have friends that love concerts, music festivals, and those types of experiences. I don't. I've had to decline invitations multiple times, and each time it was difficult because I knew I'd enjoy their company, but in the end, it wasn't worth the money for me. With that said, there are things I like to splurge on that hold no appeal to others. Find what is worth a dent in your funds and avoid what isn't, "Is this worth the financial setback?".
If you want a more concrete list, some of the worst ways to spend money (in my opinion):
Going to the movies, buying drinks out regularly, trendy home decor (that will soon be out of style), buying a new car, eating out regularly, impulse buys (of basically any kind, to include travel unless it's an insanely good deal), books you won't read (if you know you'll read them it's fine), anything to "keep up with the Joneses", basically anything that won't last.
Most of these are fairly small things that don't hurt every now and then, but I've seen people (including myself) fritter away embarrassing sums of money on some of this stuff.