Justin;
I have cut stencils myself - to do so, you want a NEW Exacto number 11 knife or similar (that tiny sharp edged point is the key for cutting tiny bends and curves, as in stencils), a hard smooth surface (I use a small "Lexan" polycarbonate block - a piece of "bullet-proof "glass"" - have also used a piece of polished "ironwood" - very hard desert wood with very fine grain - and a piece of ordinary window glass, as cutting boards), tape (unless you are using self-adhesive stencil material, in which case you stick that onto your board directly), and GOOD LIGHT.
PRACTICE and you will quickly become near-perfect! If you already have printable patterns or are able to do same on your computer, you can print your stencil-masters. I found that printing my master on plain paper as a draft allowed me to size what I wanted. I then print on to a piece of photo paper for the "real thing" - photopaper has a very smooth surface and is fine-grained paper and stiff, and can be cut with the knife very very cleanly - making for a nice, clean-edged stencil. You can also print onto other media, such as clear plastic film or "overhead sheets", with many printers, so...
But I'm actually pretty lazy, and most of my stencils are commercial AM metal things I got off eBay. There are various AM sets out there, and any metal set will provide lots and lots of panzer - markings! (When you start wearing a steel stencil out by spraying Tamiya acryl thru it, I think you may have painted ENOUGH for awhile...!

). There are also many plastic and metal stencils available in various hobby stores (including HobbyLobby) and artists' supply houses - and I have seen various stencil sets at many model shows, so your options are wide!
There are various nice number and symbol stencils routinely available on the evilbay for BIN, and I think the 10 - 20 $US you'll pay for each is a solid investment - specially if you are doing or expect to do several vehicles.
And yeah, a steady hand and calm, cool head are probably good. Maybe pass on the Starbuck's expresso-double with lots of sugar when you want to do fine cutting!
Bob