Warmoth builds that didn’t work out? Looking for mistakes made in hindsight

I would say a HUGE thing most folks overlook is the absolutely crucial step of rubbing both the Body and neck on your face either before or after you are done. Hear me now and believe me later.
I'll bite on this one. Similar to what others said. But definitely get a center punch to mark your holes so your bit doesn't walk if you aren't using a press.

Secondly... if you have roasted maple and are going to use tuners that require drilling one or two holes each such as vintage Kluson style tuners, read the literature warmoth provides which states to be very VERY careful. Select your pilot hole bit accordingly and wax the heck out of it- i.e. if the screw you have for the tuner is 1/16" (.0625) don't use whichever drill bit is one imperial size down in the hardware store drill bit set you have laying around (like you could get away with if drilling into many non-torrefied woods). Get a wire gauge #53 (.0595) bit which will leave just enough meat for the 1/16" screw to grab without splitting your beautiful roasted maple headstock right down the center of the tuner holes, leaving you with a splitting headache. Better yet, fork over the dough for the hipshot vintage upgrade tuners with the universal mounting plate and don't drill any holes. Seriously. Wish I did the research to know that existed first.

I absolutely butchered my first roasted maple neck. The headstock definitely gained some weight from all the maple dust and CA Glue I wicked into it to fix the stress fractures from doing the bonehead stuff above. I then tried to bore the holes out to 10mm utilizing the wrong style of drill bit, which resulted in tear-out that I had to make ramen to patch before hand sanding and reshaping for hours. All that went down because I disobeyed the cardinal rule of walking away when you're frustrated due to having made an error. In the end, it worked out okay, but who knows how long it will last and I bought another neck as a backup for when the aforementioned one fails. Maybe I'll post some pictures of that headstock sometime for the lulz. I've always learned my greatest life lessons by making great errors.

Final thought: don't beat yourself up. lots of us apply a liberal dose of magical thinking into these and pour hope and dreams into them, but simplified down, they're just chunks of wood with strings on them. And you're a lot more special than a chunk of wood with strings.
On my last build, I made a lot of mistakes. Had a big strand of wood lift off the body when pulling tape off, got a little too aggressive with fret files, didn't get a clean hole when drilling neck mounting holes in the body, etc.

My # 1 resource for help in fixing these issues, was Unofficial Warmoth. Someone here has experienced whatever issue you may come across, and there will be excellent advice for the fix.