@Sophie *********
the best thing to do is figure out what embassy you are going to apply at, the review that embassies website. They usually state what is required for each type of application, freelance, remote worker, soft power, dependent. There are a lot of posts for successful applications in the various facebook groups for numerous embassies, some are very detailed. You either apply online if the country you are in uses the e-visa or go in person. Several embassies have been noted to be really helpful and will review your documents, letting you know if things are missing... others not so much, so you need to chose carefully. It really is as simple as getting the paperwork together as stated, making sure you are using bank accounts not investments as that seems more readily accepted, etc.
If after reviewing all you still feel uncomfortable doing it yourself you could contact the Thai Visa Center, owner of this group, to review your documents and arrange assistance but they can't do the application for you. It isn't cheap and I'd be very careful of paying huge amounts to people who "guarantee" anything, they can't.