a). add a little extra time to projects to buffer myself.
b). not take on projects I cannot do (beyond my skillset).
c). interact with clients regularly with updates so they are in the loop, know what is going on, and constantly happy.
- Have a plan and share it, including progress updates (so they know when to expect things).
- Have an agreed statement of work (so they know what to expect).
- Think about your risks, write them down and agree them with the customer (so they know in advance that things can go wrong, and can be ready for the consequences).
- Bring up issues early, as with all the information above they will be able to make trade offs. They might be more interested in an early build with less functionality, for example.
This is just as important on a fixed price contract - although the customer doesn't carry the financial risk, they do carry a reputation risk. Every time you are late without sufficient warning they have to go to their organization/co-workers/clients and suffer the consequences of your delay. That's much easier to do a month in advance than a day in advance of a deadline.
On a): More than a little. Plan to be "90% done" by halfway through the schedule. Remember that "the last 10% takes the other 90% of the time". This is entirely true, and its due to unknowns. When this 90% at halfway approach becomes instinct, you will miss very few deadlines. This has become my internal Golden Rule for non-trivial projects.
On b): My business would never have launched if I didn't constantly stretch my skillset past what I thought I could do. But there is still a limit.
On c): Clients never like unexpected surprises. But they hate them even more if they appear late in the game. Keep expectations in line with reality.
As long as the customer is satisfied with the overall quality, cost and timeliness of the product, you've met your obligations as a business. Why does the "profit" always have to be only cash? learned skills are a form of capital reinvestment that the customers pay for just like they pay you a profit margin to do the work.