I think the most important thing is to keep learning. Expand your skills, try&#x2F;work on a lot of different projects (because bigger companies usually have dozens or hundreds of different products, teams, and roles), which means you can probably find an interesting problem and learn new things. 
Pick the brains of the more experienced engineers. Be curious. Don&#x27;t really know how something works? Ask and learn! Meeting people and network. Who knows, maybe they&#x27;ll be a cofounder with you or be apart of your team at your startup in the future.
Work on side projects and expand your interests! You usually have the time to work on side projects or explore interesting problems. I think it&#x27;s important to do them, experiment with different ideas. Don&#x27;t have ideas? Keep a notepad with the problems you face everyday. Discuss your side projects and ideas with your peers&#x2F;coworkers. Most startups usually come from a side project