I want to make customs

[Astor]

If I made customs would anyone be interested in buying one? 
Any advice as well when making one?

[tailrustedtealeaf]

I would need to see examples of your customs before considering purchasing. 
Pinned in the customs forum is a thread of tutorials to help you out in general, if you have any specific questions we may be able to help but there are so many tutorials available to help you out already.

[Blackness]

I think the majority of us make customs because we enjoy the process of creating a new pony, not necessarily just to sell them. The few customisers who have regular sales and commissions have years of experience customising.

As for advice, I agree with thetailrustedtealeaf, start by checking out all the tutorials that are available online. I also start my customs with a specific idea and colour theme in mind and I know my strengths and weaknesses - I'm better at sculpting, therefore I tend to focus on sculpting extras on my ponies rather than painting. Good luck!!