I like to recommend entrepreneurs speak with alumni (other founders of startups that have already been through Techstars) before they join an accelerator program. These are the people who have been in your shoes recently, gone through the process and will have the best insights for you.
Sometimes it can be difficult to get a conversation started with strangers, so here is a short list of questions you can ask alumni before joining the Techstars Berlin Accelerator.
This is by no means an exhaustive list, but one to get the ball rolling. Listen intently to the answers, and ask follow-on questions into points you think are interesting.