There's a few things that a successful VTC should have in my opinion.
A range of mods that other people/companies don't have. Yes, it can make people try to join just to take them, but it also gives your drivers something worth staying for.
Advertising is probably the most important thing, this is what will attract people to actually join your VTC. A high quality advert that's been correctly worded etc will get people interested. Try posting it on a few Facebook groups and on here if that's the path you want to take
You management team must work well together, there's plenty examples of failed VTC's because the managers disagreed on something and that was that.