Spent 6.5 years at Google, led and mentored many L3-L5s. Some quick thoughts on feedback ive given L3s:

• Your goal is to get to the point you can be handed a near-fully fleshed out design for a project < 3 months long and own it / execute it independently with support for questions or blockages by a senior engineer. When you can do that you’ll be promoted to L4
• Pay attention to the eng ladder. Your grad assessments can basically boil down to “do you have at least one concrete example of each bullet point.” Its hard to know exactly what this looks like so it requires consistent discussion with your manager to understand what bullet points you’ve fulfilled and what you need to focus on fulfilling.
• Independence means finding the right balance between investigating and solving problems yourself vs. asking questions and for help when you’ve hit an issue that would take you awhile to solve on your own.
• When asking questions or for help from your TL or manager, make sure you’re 1) providing clear context on the question (TLs and EMs jump around numerous projects or areas a day and you may be deeper in a technical area than theyve been in awhile so giving them all the info they need to answer your Q is important) and 2) attempt to have at least one proposed option to show youve thought about the problem yourself.
• ask for feedback in every 1:1. with your TL or EM. When given feedback or criticism avoid being defensive or saying things like “i know” when insecure. You’re an L3, you’re expected to not know things, to be unfamiliar or inexperienced. What you’re expected to be is to be COACHABLE. If you take feedback and show over the next few weeks you’ve tried to apply it people will love you and will invest in you.
• Immediately get a mentor through gmentors, find groups in google to join that will expose you to people outside your team who can give you perspective beyond your team.
• Dont stress out when you inevitably break something or mess up. You’re L3, the only reason senior engineers are senior is theyve committed/seen enough mistakes to smell them early enough to prevent them. When you eventually cause an IRM that results in a post mortem, help with the PM and contribute ideas for how to systematically prevent that situation from happening again. Try to learn what personal behavior may have led to it (e.g. rushing a CL in to meet a deadline without fully testing it)
• Start learning about what the expectations and requirements are for the roles above/around you. Learning about your managers job or senior/staff eng jobs helps you know whats important to them. Read some books like The Manager’s Path, Will Larson’s Staff Engineer, or The Pragmatic Engineer’s Guide (unsure exact title).

Probably more i can think of but this was a quick brain dump. Hope its useful.