I did an old frame years ago. Being steel, it's fairly indestructible so I used "soft" (brass) wire rotary brush wheel in an electric drill and gentle buzzed it back to bare metal. Great for most of the frame, the intricate areas I used paint stripper (in very heavy coats).
A quick rub down with some fine (400g) wet n dry, a decent couple of coats of etch primer, 3-4 decent coats of standard primer (you can also use filler primer if there are and light scratches you wanna get rid of, just means a bit more intermediate prep between coats with wet n dry) followed by plenty of coats of colour. Finish with clear laquer for a better shine, deeper colour and better paint protection......and jobs a good'un!
Spraying with rattle cans is a fairly expensive way to do it, but perfectly adequate. Biggest thing is preparation. If the area to be painted is prep'd correctly, sprayed in a dust free environment and the job is not rushed then the results can be fantastic.
Hope this helps
p.s. Just as an aside note, if you want to have a two-tone frame colour (i.e. fading, blocks etc such as BLUE and BLUE this can easily be done by changing base/primer coat colours rather than using to different top coat colours. Use a darker base/primer for the deeper coloured areas (such as grey primer, matt black paint) and a white primer for the other areas. That way, you only need one top coat colour but when sprayed over the different base coats will give a slightly different shade in those areas (if that makes sense?). That way, there's no need to mess about trying to mask areas up for a top coat paint which can be a pain in the ass, and the top coat then doesn't have any "seams" or "joins" reducing delicate areas prone to chipping.
