Usually, the way it works is that you usually simply apply. There is no rules saying you must win the top non-official tier for a County/sub-regional League to accept your application. However You are pretty much geographically locked into whatever Region/subregion you're in so if they dont have room for you or reject your application you're just waiting.

The official rule for "this is the start of the pyramid" is Level 11 meaning 10 years of back to back to back (repeating of course) Promotion will earn you a spot in the Premier League but not all of them Start that high.

For example, the Combined Countries League in Level 9(Where AFC Wimbledon started) has paths to promote from and relegate to the 14th tier. Wimbledon was granted a level 9 (CCL Premier Division) entry spot when we were formed but another club, Balham FC started in the Surrey South Eastern Combination Division One, which is