I've gotten better at it with time and so will you. Learn from your past mistakes/misquotes. I analyse each task involved in a project and estimate the hours p

I've gotten better at it with time and so will you. Learn from your past mistakes/misquotes. I analyse each task involved in a project and estimate the hours per task. When in doubt I try to split up the tasks even further. When done I add 10-20%. For me, if the price feels a tiny bit too high it's usually fair for both me and the client. If I get good ideas for extras I propose them to the client while or after delivering the initial project. Don't add it for free unless you can afford it.