During one negotiation an owner wanted to pay a general in 90 days with 15 percent retainage. The general demanded and got 45 days and five percent retainage. For subs, ask to review the general's contract with the owner and request comparable payment terms. For generals, consider hiring or designating an employee to be a full-time subcontractor relations coordinator. Respect the fact that getting the job done depends on quality relationships.
Prompt payment helps considerably to establish good working relationships.
Pay smaller subcontractors out of your own pocket even though you haven't been paid. This strengthens your negotiating position when it comes to your payment. Don't include a profit line item at the bottom of your bid. Instead build payment risks and the cost of money into each line item. This way not all your profit will be tied up in retainage.