These are things I've learned from my own vast collection of disasters over 35years (started when I was 2yo): Lost fish, broken rods, wasted money, gear failure, knot failure, near death experiences and worst of all, fishless days. The solutions I've found aren't the only answers, just what has worked for me. These are opinions, not commandments. Any other ideas would be gratefully received by us all.
If boat fishing and you see a workup (fish in a feeding frenzy on the surface, often with birds and dolphins feeding too), never troll lures straight through the middle of it. This will scare the hell out of the fish, putting them down. Instead, watch for the direction the fish are moving, get ahead of them and cast lures back towards them. You'll see a lot of other fishos doing this, and they'll be extremely ticked off if you smash through the middle of the action. You might even get to hear some salty phrases or get shot at if you do it often enough!
Avoid telescopic rods. They are an inherently delicate construction, and tend to disintegrate under the pressure of constant casts etc. One of my first trout rods was a high end telescopic that I saved for for ages when I was 11-12. After a relatively short time the top section shot off the rod. I could never get it to stay in after that, and ended up having to glue it. I've seen a lot of similar breakages over the years.
If you have one, take care of it by washing it after each trip to the salt and spraying it with protectant. If you have a genuine need for a rod that packs right down, buy a travel rod in a four piece model from a reputable brand.
Avoid the Warehouse, except for certain bulletproof items such as sinkers. You're much better to go to your local tackle shop. The advice you get there is of infinitely more value than the few bucks you'll save elsewhere. Also, you end up saving more from the local boys, as they'll work out deals for you, give you bits and pieces. Don't be afraid to ask them dumb questions, we all started as noobs.
Braid fishing line is wonderful stuff, but it's expensive and can be tricky when you're starting out. It's only really essential for reasonably specialised techniques like softbaiting, jigging, poppering, and if you're only baitfishing off the shore or a boat, you're better to start with monofilament (nylon). You'll tend to get a lot of tangles and snags when you're new, but as you get more proficient, these should diminish. Then you're probably ready to invest in braid.