The best advice i've ever had for this is to just turn it around, and imagine you are hiring someone to build stuff for you - how would you want an ideal candidate to behave? Now work hard at making yourself that ideal candidate.

The second most useful advice is to consider the power dynamics in your relationship, as it is not always the direction you expect. The best long term relationships work when the client and the contractor have as much to gain from the success of the project as each other.

And best of luck with your new venture. Exciting times!