FWO application process
It's all pretty well explained on their website.
Psychology
Writing a grant proposal is at least as much about psychology as it is about science. The people grading your proposal have too many proposals to read and assess within a rather short time window. Which means that your proposal can be their fifth to read at the end of a day when they're getting tired and their mood isn't as good as it was in the morning. So please, think about how you would likely react if something is not clear from the start. Indeed, your initial reaction may very well be along these lines: 'Now, if the guy/girl asking for money doesn't even bother to make it as easy as possible for me to understand what they're about to do, then why on earth should I bother giving a good grade?'
While this may come across as unfair, there's only one advice we can give: get over it and make sure that you submit a high-quality and pleasant-to-read proposal!
Points of attention
For each grant, the scientific section is not the whole work. You also have to justify why you are the best candidate to perform the proposed work. For a postdoc, and certainly a senior postdoc, for example, qualities that are looked for include independence, providing guidance (co-promoting master thesis students and/or PhD-candidates), international mobility, the size and diversity of your network, ...