There's actually a book on this topic from the guy who did Dothraki for the GoT show. Haven't read it yet though I did buy it at some point. (no affiliate link)

https://www.amazon.com/Art-Language-Invention-Horse-Lords-Wo...

FontForge has a tutorial: http://designwithfontforge.com/en-US/index.html There's also a basic introduction to font design in David Peterson's book: http://www.amazon.com/The-Art-Language-Invention-World-Build...

I've been meaning to learn how to create fonts for my own conlanging purposes for a few months now, but haven't quite gotten around to it yet.

Here it is for pre-order! http://www.amazon.com/Art-Language-Invention-Horse-Lords-Wor...

He told me it covered the essentials of language construction as far as his methodology goes, but I think it offers some insight into the development of other major and not-so-well-known conlangs as well.