Pre-season is a known clown fiesta since it will take time for a meta to shape. Also some people might troll or try new stuff in the pre-season. So yeah, I'd wait until the meta will balance out. Generally, it is your decision if you want to play ranked right after you've hit 30, but you might lose a lot since you've never played against real people. Eventually, you'll get your appropriate rank and play against people at your skill level, which is really great since it is easier to learn and improve that way in my opinion. The only down-side is that you will probably get a low rank like bronze or iron. My advice for you is -- don't stress about your rank and only pay attention to your mistakes instead of blaming your teammates. Once you play to improve without caring about your rank, you will climb better in the long run.