The biggest help is to not need work. When you have a financial cushion, it's much easier to say no.

tl;dr: Hitting rock bottom twice.

Started as a freelancer, got too many projects at the same time. Could not meet any deadline and got burned out. Everybody lose.

Build up a small dev team, got too many projects again and got a single person working on three projects at a time. Same thing: long days, too little progress, could not meet deadlines. Everybody lose.

The issue with dev work and switching between projects is that is takes a few minutes to an hour to focus and get really productive.

With experience you will find what is the equation that works for you. In my case I do not do more than one dev/code work at a given time or quality starts to degrade.

I can provide consulting, answer questions and do estimes on other projects while coding, but only one dev work at a time.

Know thyself. Find a niche and develop an appreciation for the value of your work. Only if you know what you're good at and if you have the self-esteem to say so will you be able to say no to work that doesn't suit your profile.