Tier 10 is hard as balls when you first start playing because the entire carry potential is on your back now. There's no longer a top tier to bail you out or someone to hide behind, meaning that any mistake on your part is felt by the entire team. It's probably even worse in this regard with the new MM, where there are fewer 10s and way more shitters in 8s.
I mean, my Ehundo was rolling around with a 45% WR or some shit for the first 100 battles and the fact is that after 466 battles, it still hasn't cracked 60% even though it's close. Your first 10s are going to have trash stats and that's fine because you're learning. If you ask around, you'll find that a lot of people here spent quite a bit of time grinding their old pubbie tanks up to par.
I can't say much about the current T10 meta because I'm still re-learning the game and maps at lower tiers but I'm sure it's still a shitfest. The most important lesson is probably going to be positioning and how to approach engagements, now that you can't afford to throw away your HP. Don't be afraid to pull out of a shitty situation before it becomes totally fucked because you are worth more than most of your team is. Also, don't forget to spam the shit out of prem shells. Tier 10 is the land of enforcing your will on others, which is very expensive.