Toby Stone just explains the what, how and when of accelerators.
In a nutshell they should be a good fit for your business before you join one. You shouldn’t do one if your main need is simply capital. They may take equity or some other parallel. They provide you with mentors who have been through it before. Ideally this mentor and your investors should have specific knowledge but also general knowledge that you don’t have and can benefit from.
An accelerator like an investor is way more than just the money and you should spend time trying to find a good fit. There are some specialised ones.
SeedDB is a great site that lists them all but they are constantly changing. There are some more specialised ones like Healthbox and TechStars
A note on Crowdfunding: Seedrs will manage the crowfuding investors for you, Crowdcube won’t.
One of the best ways to fill your funding round is to use different platforms at different times to lure in different kinds of investors at the right times. For instance Kickstarter is really useful to raise awareness if you have a hardware product. Then when, your round is filling up it gives you momentum and clout when talking to angels, however, this is only one example and every different situation will require a different strategy.