Strange New World, despite being a prequel, is a great place to start. Deep Space 9 is also really good for learning about Star Trek, and it’s probably the best written overall. You could also watch a Best of the Next Generation marathon. I’d recommend that over watching the whole thing, because TNG really shows it’s age sometimes.

The most important thing to remember is that most Star Trek shows take a little while to get off the ground. They usually find their feet around season 3 (that’s when Riker grew his beard).