I'm just having some fun here, but who knows, maybe some of these things can be helpful to new builders. As a 30+ year veteran of this wonderful hobby, I have enough hindsight now to know what I was doing wrong in 1988 when I committed to making this a hobby that I wanted to pursue long term. Here's my initial list:
1) When you brush paint parts, wait for them to dry before proceeding. Seriously, wait for them to dry. The same goes for spray painted parts. Fingerprints never look good on your completed build.
2) Along the same lines, when you're using plastic cement (as opposed to super glues), wait for the glue to dry. Sure, you can continue on, but you're just going to fight with parts that refuse to stay in place.
3) When it comes to cleaning your brushes, paint thinner is paint thinner. If you're using enamels, a large tin of Walmart thinner is just as effective as a small bottle of Testors thinner - and the price is almost the same. I wasted so much money on small bottles of Testors thinner! This applies to lacquer thinners and acrylic thinners as well. This doesn't apply to airbrushing, which leads to...
4) Use a compatible thinner to thin your paint. It doesn't have to be from the same manufacturer, but if you're going to go rogue, test the paint first before committing to your actual build.
5) If you screw up and decide to trash a build, don't throw it in the garbage. I look back on so many abandoned builds where I now realize I could have raided those disasters for parts.
6) Buy good tools, but don't feel like you have to buy EVERY tool right away. Sure, it's nice to have an array of knives, files, sanding sticks, brushes, paint, etc., but in the process of acquiring that, lots of cheap crap was purchased. I now have a good assortment of quality tools and it really does make a difference. Those cheapy Harbor Freight tweezers might look good but once you realize they have very little clamping strength, you understand that you should have spent that extra $10. Nevertheless, those cheapy Harbor Freight tools still have their uses. Some of them might even keep your bag of Doritos closed.
And for now, my final bit of advice to myself:
7) Be fearless. I waited so long to use an airbrush because I was afraid of not using it properly. I never tried weathering because I was afraid I'd ruin the model. I was so scared of getting paint runs that it took a long time before I got close enough with a spray can to get an actual decent gloss coat without orange peel. Mistakes happen. If you aim for perfection from day one, you will fail. Yes, you will see amazing builds online and at shows, but what you don't see is that those builders made all of the same early mistakes, they just powered through and got better.
Feel free to add to this if you want to. I was working on a kit and got frustrated at one point because two chrome parts were not adhering so well. In the past, I would try to force this, but experience let me know that it was because I hadn't shaved off enough chrome from the two parts. When I went back and cleared them more thoroughly, the join was near perfect. That got me thinking about what a moron I used to be - impatient, frustrated, angry... none of those things made me a better builder.