You can also print out a nice roman letterstyle from your computer, tape it onto a piece of glass, and try to replicate it.
That or pounce patterns are a good start.
I find the sans serif styles much harder to make look "right".
I just faked it till I made it and I still fake it here and there.
After a while you get so used to letter forms that you don't need a cheat sheet.
And you get a few basic alphabets in your head that you can crank out on autopilot.
The key is practice practice practice.
Turning your finished piece upside down helps the mistakes stand out like sore thumbs.
Also, remember that round letters are always bigger than straight ones or they just look wrong.
Remember that in a thick & thin letterstyle the ones with the thin strokes first are M A N.
I never thin my paint very much because it gets too drippy, and if I do thin it I use turpentine.
Those tips are probably not very helpful but they are what popped into my head.
Love....Jill