I've been a Tech Lead for a year now. I'm still learning but some of the things I've done which I think will help are:
1. Start by setting up the development environment and getting the software you'll be working on to run locally. Then, fix a couple of easy to medium level bug fixes as soon as possible. This is the fastest way to learn what your team is talking about.
1.5 If you don't understand something that's being said at a meeting ask, but don't hijack the meeting, make a note and talk to someone who can explain in more detail.
2. Think at a high-level -- what is the product supposed to be doing, abstract away -- some engineers will talk in code -- which you may not understand early on but interpret what they're saying at a high-level.
4. Be available and approachable to everyone on the team.
5. Understand the impact of a bug fix or a feature -- how much QA effort does it require, what is the operational impact of the work, does it break backward compatibility etc.
6. Participate in product meetings and consider designing any new features as homework so you can better discuss it with the engineering team you're leading.
Good luck!
Edit
Some DO NOTs:
1. Do not complain how bad the code base is. No one likes someone new walking in and saying that at once.
2. That said, understand what technical debt there is and address it incrementally. Don't say "we should re-write XYZ."
3. Do not suggest alternate platforms and frameworks unless is absolutely makes sense -- this is especially true if the team is big and no one knows this new framework besides you. You need your existing team to contribute to and maintain projects.
1. Start by setting up the development environment and getting the software you'll be working on to run locally. Then, fix a couple of easy to medium level bug fixes as soon as possible. This is the fastest way to learn what your team is talking about.
1.5 If you don't understand something that's being said at a meeting ask, but don't hijack the meeting, make a note and talk to someone who can explain in more detail.
2. Think at a high-level -- what is the product supposed to be doing, abstract away -- some engineers will talk in code -- which you may not understand early on but interpret what they're saying at a high-level.
4. Be available and approachable to everyone on the team.
5. Understand the impact of a bug fix or a feature -- how much QA effort does it require, what is the operational impact of the work, does it break backward compatibility etc.
6. Participate in product meetings and consider designing any new features as homework so you can better discuss it with the engineering team you're leading.
Good luck!
Edit
Some DO NOTs:
1. Do not complain how bad the code base is. No one likes someone new walking in and saying that at once.
2. That said, understand what technical debt there is and address it incrementally. Don't say "we should re-write XYZ."
3. Do not suggest alternate platforms and frameworks unless is absolutely makes sense -- this is especially true if the team is big and no one knows this new framework besides you. You need your existing team to contribute to and maintain projects.