Guide to easy experience gathering
If you join a location that is currently being occupied by higher level player, and you play smartly and cooperatively, you'll not be any hindrance for the goals of this high level player, and you'll be able to cut your slice of cake without reducing anybody rewards.
It is recommended that you pick up every beer bottle you stumble upon, and that you transform all of them into molotov cocktails. Molotov cocktails are the cheapest way to speedtrain your character. You get the exp and item rewards for dealing any noticeable damage to the monsters. The monsters which might be unbeatable for you, might be dying from a touch of this higher level player. All you need to do is make sure you dealt some damage, and you can reap all the rewards, with molotov cocktail, if you see a congested point full of monsters, you throw in one, and you might get a return of investment over 1k experience per molotov if you place them right.
Your goal is to tag, and you want to use anything that lets you tag cheaply. The easier for you it is to do a little bit damage to the opponents, the easier for you is to reap the benefits of work done by others. The best in the game is Tesla rifle. Every character needs a Tesla rifle just for the purpose of tagging opponents, in case they're around other players, don't want to be a dick, and don't want to one-shot monsters, Tesla is the way to go, but unfortunately it has level requirements, and most of early weapons are slow and low magazine. The best cheap low-level mass-tagging-tool is molotov.
There are certain locations in the game that spawns PA frames. Some of these locations are spawning level 15 Raider Power Armor frames, and this is the lowest level power armor in the game. Power armor chests can be modded with "Tesla Coils", and that deals small amount of damage in AoE from the wielder of such armor. You want to get yourself a piece of power armor chest as soon as possible, and you want to use some forums or discords to ask someone to mod it with Tesla Coils for you. I trained new character, and I was doing an event, One Violent Night. My dog started demanding that we go for a walk, so I left my character nearby the lure that summoned the monsters inside, and near the doors, and I went with the dog. I returned, and my character was two levels higher than I left it. The AoE effect tagged each entering ghoul, the other players took them down, and my character has been accumulating experience simply for being there. If I didn't lose the exp for ghouls that went through other entrances, I'd have four levels in that period. You want to get yourself hold of this armor, then you want to follow higher level players, running around and luring monsters to them. You'll vastly outpace the amount of experience you could gather alone, and you won't have to spend a single bullet to do it.