get to know others in the building community -- a few rapid suggestions --
EMRFD book by W7ZOI and others -- out-of-print at the moment
Soldersmoke website and podcoast
Websites of K8IQY, AA7EE, N5IB and others
Start small on your homebrew projects, and work your way up. Also consider modular construction on smaller boards, so you can more easily make changes -- and re-use modules.
get some basic test equipment -- some of it can be homemade.
join EMRFD and QRP-Tech yahoo groups.
learn from others designs -- even the one's kitted.
learn from your own errors and difficulties -- when a project goes perfect, the opportunity to learn is less.
don't fret what you can't purchase or find -- collect the most commonly used parts and gather/build some useful test equipment. a signal source can be a simple xtal oscillator, a power detector can be based upon a diode detector -- or commercial log amplifier.