Read.
Read a lot.
Read as much as you can.
Read from
this site,
Double Bass Chat, The
Art of Slap Bass and other bass sites.
Read the manufacturers' sites. Read what the jazzers use and read what the psychobillies use.
Read what the bluegrassers use, read what people in other genres are using, even read what
bass guitarists use.
While reading, answer questions such as:
What kind of music will I be playing with this gear?
What do I need? What do I want? What can I afford, new or used?
Take your time with it;
Wait for the right deals to come along;
This way you will get what you want, need and can afford for the type of music you're playing.
At least that's what I did. I decided on and bought a pickup (alas, not on sale).
Then I bought the preamp/DI I thought was right for me (on sale). I gigged with venues' amps &/or PA support.
It took a long time to find the amp I was after, but well worth the wait as I got it at nearly half price! For now, it matches all my needs.