I typically play fast and wild with my fabric, both with my scrappy style and although I started out being very precise, for the last 20 years or so I use the cut/sew large and trim down techniques and things like making HST out of full squares of fabric -- something I used to snort down my nose and derisively refer to as "fabric wasteful" techniques. When I started analyzing things I found I wasn't really wasting all that much fabric (sure, some!).
I will draw cutting layouts and figure out things like if it makes more sense for rectangles to be Up/down or side/side orientation. I have certainly pieced more than one piece because the fabric was less than I thought. Read the bolt ends and measure (I keep a tape measure in my purse), although I grew up when fabric was 44/45" I no longer count on anything more than 40" usable -- if I get more I'm happy but I've had enough projects made difficult because I really needed 42.5" or whatever it needed to be and just wasn't there.
When you are cutting right triangles, you can narrow down the strip width so that one point is already snubbed off, it you have enough rows that extra 1/4" can turn into an extra row.
Measure repeat times! You can only cut once... I keep a roll of 1/4" quilters tape in my kit and will often put a piece on my ruler to reinforce the cutting line and to help in my cutting accuracy.
While talking about only cutting once, it's something I'm working at which is replacing my rotary blade more often than I do. I try to buy on sale/in bulk but I still feel they are "expensive". But even a full price $5 blade is a lot less than cutting up $100-350 worth of fabric badly.
I haven't been able to afford quilt shop fabric for most of my life, so I've always bought the sales and clearance fabrics. I'm trying to not buy any fabric any more except what I have immediate need/plans for -- no more buying just because I like something. Most of what I do buy is from thrift stores, I go out on a regular basis/route and never know what I'm going to get or how much there will be, but at $1-3 per yard/bundle, I can get a lot and some days I do while other days I come home with nothing. My Seattle area is relatively affluent and I am able to find all the quilt shop brands, along with a lot of Concord VIP type fabrics. You find yourself a lot more open when the fabric isn't $12+ per yard.