A.M.C.
The above advise is sound, and clearly comes from those who have experience in this field, but I wonder what "qualifies" you to manage the investment a principal makes in his aircraft, and quite what it is that you believe you can offer him by way of a management service.
Your reference to "airlines" getting clients makes me wonder, but if you are under the impression that it's just a bit more work than simply flying the airplane, you are very much mistaken. Be assured that most (but not all) principals (private aircraft) have a fair understanding of what is required, and if your knowledge is lacking, they will soon suss you out. Bear in mind also that there will be other (maybe more qualified and certainly more experienced) management companies chasing the same client - and there is a good chance that some of them will certainly know what they are talking about!
Getting the contract requires a good degree of salesmanship, a good degree of knowledge, and a good degree of good fortune (too many good's in there perhaps?), but KEEPING the contract requires a high degree of service, knowledge and cunning. There are many out there only too anxious to steal an already "set-up" contract - and some scumbag Captains you employ are the first to watch out for, so be warned.
It may be that your "investors" would be interested in you purchasing an existing contract. I'm not permitted to advertise here, but it just so happens that I have one client too many at the moment..........a charming gentleman, an on time payer and a pretty quick jet that's only two years old. I wish I could tell you more, but pprune would charge me for the ad!
I hope that is of some help, and happy hunting!
Sooty