Yeah, you got it. It's not just presales, there isn't a big difference between buying in a presale and a regular sale. Presale just gives you two shots at it.
The tickets are first come first served so whoever completes the CAPTCHA fastest gets the best tickets. However, some will always be released when people don't actually complete the transaction. So you can keep trying again and again for 15 minutes or so. Whatever you do, do not try to buy different tickets at the same time on the same computer. You cannot buy tickets for two cities at once, you will lose all your tickets. You need a VPN or your cell phone internet if you want to start playing that game.
The best way to decide on a show is to look at the listings on Stubhub for a show by that artist that is already on sale. Assume that to sell a ticket you need to beat the lowest price on Stubhub. This isn't always possible and that's where your intuition comes into play. If you're in doubt about whether or not to purchase, feel free to email me and ask. For now, Leonard Cohen is a really good one to start with. The presale passwords are easy to find on google. Phish will also be announcing more shows soon and they are just about the hottest ticket this summer.
In a small theater, any seat is good enough. In a pavillion, only the front sections or the front of the rear sections are ok. The back of the rear sections in pavilions are a trap. Lawn tickets usually don't have very good margins. In an arena, anything that isn't behind the stage is usually ok. This is because in a pavilion the rear seats are usually the same price as the front seats, but in an arena the upper seats are significantly cheaper.
I haven't had a show yet where I have lost money, but I make my picks carefully. 200% profit isn't very common though. 50% profit is probably a realistic average. I may end up getting rid of Billy Joel/Elton John tickets soon at just a little over cost.