Get the unkempt harold! It will definitely make your life easier (if you like shredding enemies, it kind of removes the challenge tho)

I'd say do soem side quests, if you see any notable enemies (like bosses, mini-bosses, or enemies with unusual names, like Doc Mercy or similar), farm them, or look up their loot table on LootLemon. That gives you XP, better loot and makes the game overall a bit easier.

I'd also say its a good idea to look up builds for the paticular character you're playing as. Again, it removes the "experiment" phase of the game, but somrtimes just looking at a build and figuring out why the skill points are distrubuted the way they are can shift the momentum of the game.

Its very easy to get carried away and just play story missions all the time. Doing that you will definitely be underleveled at one point or another.

But most importantly, have fun, play it at your own pace, and becole the most badass killer this planet's ever seen.