I may only be 15, but I consider myself quite the avid concert go-er. I've been to about 14 concerts (although I probably left out one or two), and a variety of venues; whether it's a stadium, an amphitheater, or a smaller indoor venue I've seen it all.
Stadiums are going to be the most expensive overall. Your seats, the merchandise, the food, the drinks, all of it; be prepared to spend a lot. A reminder, however, is that typically because of it's size any seat in the house will do. There's going to be screens, and if you're like me and you're short, sometimes being higher is better if you'd like to see. The GA/floor level will always be the most expensive at stadiums just because they're closer to the stage, but you also have to worry about losing your spot if you need to pee, or just not being able to see in front of the random person in front of you. Another thing to remember is that on the floor it's going to get extremely hot very fast, so dress appropriately and if you're even the slightest bit claustrophobic than you may as well say goodbye to anything GA related. Moving up, next you'll have your 101's, 102's, and 103's. These sections are great overall because they're still low but not as expensive. Then the numbers just continue to grow the higher up you go. Obviously the nosebleed section will be the cheapest. I was in the nosebleed section for One Direction and Green Day both were absolutely amazing experiences so, in a stadium, where you are doesn't really matter.
Amphitheaters are large outdoor venues. Half of the space is usually under a over-hang and the other half is lawn. Amphitheaters are still expensive but as far as concerts go, they're on the cheaper side. With seating it's pretty much the same deal. There's GA, which is smaller because amphitheaters aren't nearly as big as stadiums, 101, 102, 103, 201, 202, and 203 (usually), and then lawn space. I recommend 102 because, once again, it's reasonably priced for where you're located. 102 is a center section (usually), and its right behind GA. You have seats, and they're staggered so you have a great view pretty much wherever you are. The lawn has screens everywhere so it's not like you won't be able to see, however my personal preference is 102. I've attended most of my concerts in amphitheaters (5 Seconds of Summer, Blink-182, OneRepublic, Billy Joel, Maroon 5, Niall Horan, Jonas Brothers, and the list just continues). The only draw-back to an amphitheater venue is that, because it's outside, inclement weather may cancel or change your show date. So keep that in mind depending on where you live and what time of year it is.
Small Indoor Venues
These are my personal favorite because it's all standing room only and you just get a more intimate experience with the artist. They are a little pricey but most of the time it's just merchandise that will get you and thats really all up to whoever is selling it. Standing room only venues are a lot of fun. Try and make friends with the people next to you because you never know what could happen. For example, I made friends with some people in front of us and when the artist came out, because I was so short, they let me stand in front of them. Just keep kindness in mind. Also, be prepared for some not so nice people. I went to a show two months ago and the people in front of us were so nasty that when my friend and I went to move past them they intentionally blocked us and then yelled at us because they thought we were going to take their spot. So you never know what kind of people you will meet here, bottom line: just be nice. Getting to the front is difficult. If you want to get to the front either get there early, or follow someone who's moving through a crowd. My friend and I have also traveled up the side and cut into the front, it was effective but we both felt bad because it was inconsiderate to the people who were behind us who had waited all day. So don't be like my friend and I. At this type of venue I have seen The Neighbourhood and Pierce The Veil.
So aside from cash, and seating, regardless of where you go always dress appropriately. My go to for any concert is a thin t-shirt or tank top, a pair of jeans, and some good walking shoes, since you'll be on your feet all night. I also recommend (if you're a lady) to bring a small purse and designate it for concert use. Accidents happen and you never know when a drink could get spilled on your purse so it's best to get one specifically for concerts so that you won't care too much if it gets ruined. Make sure your phone is fully charged, if you're like me and you like to take picture and videos, I know most venues prohibit the use of most cameras, so if you're unsure just take your phone. Finally, don't spend the whole night watching the show through your screen. I know it's tempting but trust me, when you get home you'll be happy that you sang along and danced instead of just seeing a bunch of videos of songs you wish you had danced to. So just have fun. The night is about YOU seeing an artist YOU like, don't let others disrupt that and don't ruin it for yourself.