Freelancing is the domain of accomplished, reputable, and HIGHLY-trained musicians. The last one (well-trained), means you have the musical skills (understand the academia of music.. harmony, theory, etc), can read music really well, follow chord-charts, you have great time, you have well-developed ears, have a deep understanding of different styles and can play them authentically, have the technique to pull off anything reasonable. You DONT need to have technique like Victor Wooten, but you do need to have technique to emulate styles, and sounds as per the repertoire you are playing. PLaying a wedding gig and doing Earth Wind and Fire tunes... can you slap in the 70's style?
You also should have the equipment necessary to support any kind of gig or situation and that equipment is reliable, AND you have back-up gear. You bring equipment that is appropriate to the situation. You are professional to the highest degree... you show up on time, ready to play at the start of the gig, you know the tunes (ie no fumbling around, no wrong notes, no arrangement snafus), you are interpersonally easy to work with, not a prick, dont talk about other musicians disparagingly, you have reliable transportation. About tunes, you need to know a lot of tunes, by memory. There is a basic gig repertoire for each style of music, jazz, classic rock, R&B, etc., and depending on your aspirations, you need to know hundreds, if not thousands of tunes, on the spot. Also, you need to be able to play in different keys. I could go on and on, but the bottom line is: You take a gig, you show up, you play, you go home, you've done everything perfectly with no excuses... that's your goal as a freelancer.
Assuming you are these things, the answer to your OP is..... Gigs, gigs, gigs... take every gig that is thrown your way. Assuming you play your ass off (see previous paragraphs), you will get called back AND MORE IMPORTANTLY referred for other bands, situations, gigs. Play each gig as if you want the person hiring you to say afterward: "Yeah, call that guy if you need a sub. He just showed up and killed it. He was a nice person, He had no attitude. He had no excuses... he just played his ass off. I have no negative comments about that guy". Your self-assessment needs to be honest. If you played a tune, and you screwed up the changes, or the form, you need to drive away angry with yourself, and go home and fix it.
If you start doing the above, I guaranty you will slowly begin to achieve your OP goal. It will take time.