Some rules of thumb that I’ve accumulated during the last 3+ years as an independent product management consultant:
Always include several options in proposals, ideally three choices that are good/better/best.
Always provide a discount for full prepayment, ranging from 5-10%.
Always include a late payment penalty in the contract
For clients that are hourly or that pay for a distinct service on a regular basis, make sure to raise rates by a certain percent every year. Officially notify them of the rate change about 2-3 months ahead of time.
Aim for at 3 lunches/coffees with strong prospects per month
Don't hire sub-contractors who are not true independents but are just between full-time jobs. These folks have too much of an "employee" mindset and require low-level direction, where real independent consultants take the ball and run with it. Also, "employee" types also tend to file unemployment claims because they don't understand the legal definition of independent contractor.