Focus on why you need from the accelerator, and make sure that need is being met, don't let the lure of "help" from an accelerator blind you to mismatches between your goal (making "Startup X" successful) and the accelerator's pre-programmed processes. If there is a mismatch - be very careful.
The gory details:
It might help to know why you selected a "startup accelerator", and to differentiate between the kinds of programs. By "accelerator" I assume you are talking about an organized and funded operation that provides one or more of the things startups have trouble getting - advisors, investors, office space, employees, education (management/marketing job skills), manufacturing, etc. - these can be very helpful if you are in a position to make use of them. On the other hand they can also be a huge distraction if what they offer is not matched to your organization.
Back in the early 2000s, I allowed my partners to get our startup to join an "Incubator" (an ancestor of today's encompassing "accelerator" programs). This program had office space, some minor and essentially frivolous benefits (like cheap printing - something you can get from Kinkos), and a mentoring program with a process of matching you to a board of advisors. It was an alluring idea, particularly since none of the partners had ever held a CEO title before, and we thought that this program would help us mature. The problem was that as soon as we started accepting their "help" we became captive to their interests, and not our own goals. Ultimately I think we were too small to work with them, because everything that was our startup identity was swamped by the paternalistic "help" they were prepared to offer.
We were also a very small startup with 3 people, when most of the other companies in "the program" had tens or more staff. As far as the incubator was concerned, after we signed the agreement, we were just one more potential win/lose, and as time went on we never grew fast enough to garner more than cursory attention. Most of the products they offered we couldn't take advantage of, and the few fits like matchmaking with advisors was a shambles, the incubator managers air-dropped a team on us that was very poorly matched.
In our case, the hand-picked "advisors" immediately disagreed with our idea, arguing that what we wanted to do would never work, and that they knew better markets than we did. In the end, the partners decided to accept the advice, and we pivoted to pursue someone else's ideas. The downside was that the advisors who knew those ideas best, and would have been excellent partners, were not actually invested in the startup, and arms-length advisors will never be as committed and involved as you have to be to make any startup in any market successful. Note, our ideas did see light of day in the market, and success, with a different company, so much for the vaunted "advisors". Be careful of "free" advice...
To put it bluntly, no one cares more about your startup than YOU, no accelerator or incubator can match your passion for your idea. When you agree to let an outside organization guide your startup, now you have agreed to let someone else into the decision making process. Ultimately, an accelerator may be a very good idea, if you are close to market, you have a strong grasp on your team to ensure they wont be captured by the accelerator's own goals, and you are looking for specific outcomes. Remember, what was worth pursuing before the accelerator came into the picture should be driving your decisions, not what the accelerator can do or wants to do. Don't let "advisors" become directors or pseudo-CEOs unless they literally join and invest in the startup - and always remember, only the people with money on the line (you) actually care about your success or failure.