To be fair I've only ever had verbal contracts for most of the films I've scored, but for anyone who wants to play the game sensibly and seriously:
1: Contracts are vital, Always read them, especially NDAs. They keep things controlled, sensible, and you don't get smothered in scope creep. Make sure that they are reasonable and fair.
2: Never completely trust anyone you do with business with to fulfil their end of the contract. Even people you've worked with for years can become unreliable fast, especially when it comes to payment. It's a business contract and very different from friendship.
3: To prevent losing a company to bankruptcy from people going to focus groups for sandwiches... Make them bring a packed lunch.
Solid advice from someone who is industry burned regularly:
Avoid Politics if possible. Whatever side you take, it alienates someone who will make trouble.
Even if you just communicate with emails, ensure you keep them so you have evidence that you have an agreement. This is still a contract of a sort.
Get 30-50% Upfront from someone. Martin Bower recommended 50% to me, and he was an industry titan modelmaker. If you are doing marketing, do NOT put your own money into anyone's campaigns, get ALL the adspend up front additionally.
If you're doing work like music, ensure to send basic samples first. This way you can find out quickly if you're doing the right thing or not. When I scored Decline, I worked on the soundtrack for 4 months before it got scrapped because the director liked a completely different style of music. A drum beat for tempo is great. I use a 120 and a 140 of basic kick snare with a single note up, and down so things can be edited to how they will be when the film maker wants to score.
Always prioritise people who have your back over people who are flaky, even if the rewards appear better.