Yeah, it's definitely not easy...
I try to get each job done as fast as possible. I also keep a team of freelancers on hand who I can call on a whim and get fast turn around. (All while maintain very high quality).
Also, I prioritize by how much money is riding on the deal and how long I expect it to take. If I have a $10 customer vs. a repeat $1,000+ customer I might give preference. I try to be as fair as possible and usually calculate the work load of each task while making the deal. I then outline where time is going to be spent first.
If I need a small job or one that's time consuming I will give the job to a friend / biz partner to get done that way it's delivered with quality and on time. I may lose money from giving the deal to a friend but it's good for avoiding bad business relationships...
You just need reliable, honest, and trustworthy people. You also need to be honest yourself because, if you screw a partner over and need them in the future you've already burned your bridge(s).
I also do networking and have built up a network of trustworthy businesses whom I work with from time to time and we do "load balancing" from time to time. As well as share knowledge, do favors, etc. Basically, we just try to make it a win-win for everybody.
I'm frequently on AIM so I always have friends inspect my work before sending it out to clients and I ask for ideas, suggestions, etc. This helps me make sure I deliver high quality and don't miss certain things.
I often also, have long conversations with clients and business partners and I make sure I know every detail... How they want it, when, budget, etc. Unlike many designers who just build a layout for awebsite and say here you go I take the time to talk with my clients...
I ask what are your business colors, what colors do you want in the site, are there any other websites you would like to model after (perhaps they have some great feature), I find out what kind of image they are trying to project, target audience, and just about everything. I also document everything they say so when it's 3am and I'm trying to remember that one last thing I just reference my word document that has the clients request and make sure everything is completed as they want it. I also work with the client and if a change needs to be made I make it. I also do post-work making it so that code is optimized, secure, and cross browser compliant.
By doing all these things it prevents headaches, reduces later changes, increases the clients happiness and leads to repeat business.