These are in no particular order of importance, just as they spill out of my brain....
-Find an organizational system that works for you. Finding your stuff is half the battle. Not buying something twice is important, although if you do, you have more to use.
-Figure out how YOU like to work, and structure your bench(es) to make that happen. For instance, I like to have an "L" shaped workspace, so I have to workbenches set up in that manner. I put my powder dispenser and scale on one bench and my press on the other...that way my press doesn't jiggle the scale around.
-If you're using a balance scale, put it at eye level to how you'll be when you're loading. If you stand, put it at eye level when you're standing. If you sit, then get it eye level for that. Putting on the bench surface means you have to lean down to check it each time. That is not fun. Trust me on that.
-Get a few manuals and follow them. But also ask questions and learn what to look for to identify when you're at max....for your rifle. That may or may not occur where the books say it will. When you read about people being able to load "over max," that's misleading. They aren't....they're (hopefully) within safe parameters for their rifle, but it may exceed the book's max charge for that powder/bullet/cartridge. Learn the book, but then learn what the book's functional limitations are.
-Once you've made a bit of ammo and feel pretty comfortable with your reloading processes, think a lot about picking up QuickLoad software. Do not do this as a newbie, but when you've gotten pretty well tuned up, then think about it. It is a little pricey, but it solves a LOT of frustrations you may encounter. There are no shortcuts in learning.....you need to hit the frustrations the way we all do, and then think about QL and it'll pull back the curtain on a whole new world.
-Don't get in a hurry. Haste is the breeding ground of problems...both minor and major.
-Don't use someone else's reloading data until you know you can verify its safety in YOUR firearm. Period.
-Don't reload for your friends until you're ready to take on the responsibility of what happens in their firearm with your reloads. I will reload for my father. I feel it's the least I can do for what he's taught me over the years. I will not reload for anyone else.
-Don't expect to save money with this hobby. If you want the lowest bottom line, find the factory load your firearm likes best, and buy a lot of it. Then never spend a penny again and you'll be money ahead. A guy with one rifle who shoots half a box a year isn't going to be well-served by handloading ammo.
-There's a widget for every reloader, and they all cost money. Don't buy all the gadgets. At least, not right away. I have my share of tools and equipment, but there's a lot of chafe to separate from the wheat. Only you can know what will serve you well, but only after reloading for a period of time with basic gear will you really know where to spend the money to make reloading more enjoyable. I could list my stuff and why I like it, but that's all MY likes and won't necessarily be the same for everyone.
-Keep records. Do it somehow that makes sense for you, and don't lose it.
-Bigger isn't always better. Faster isn't always better. Don't get stuck in that mindset.
-Don't even bother discussing reloading at the range. Everyone is an expert, and they all know more than you. Don't believe me? Just ask them. They'll tell you everything you're doing wrong. The fact that you're shooting groups and their targets look like they're patterning 00 Buck with a cylinder choke doesn't dissuade them from telling you what you're doing wrong. Just don't engage in the conversations.
I'm sure I'll think of more, but that's what I got for now...