Start off with the bare frame completely stripped of old paint. Use a lint cloth before spraying on 2-3 base coats of primer (primer for steel frames). Use a very fine grade of sandpaper (400 grade) with a bit of water over each primer coat. Wash off any primer dust debris with water, let frame dry and go again with a lint cloth before spraying in a colour.
Do two to three coats in your preferred base colour from cans (I prefer Kobra, Montana and Molotow brands - i find them superior to the costly Spray.bike cans). Use frog tape for any masking. Splatter can be done with acrylic paints from a tin and using a toothbrush or long paint brush. When all dry, apply decals and then lacquer with 2 coats of 2-pac Lacquer from spray can. I find Spraymax 2K Clear Coat - Gloss - 400ml is one of the better ones.
When lacquer is hardened (after a few days) polish with Meguiar's Cleaner Wax. It'll give a snooker-ball like shine and protective coat.
I've always used
https://www.fatbuddhastore.com/ for my home spray paints. They are very quick turnaround and reasonable prices.