Dan Ryckert's been getting a lot of crap lately on Twitter since he's been talking about his difficulty in finding a new pair of jeans. But the truth is, finding a good-fitting pair of jeans isn't quite as simple as going to a store and finding something that just fits. I'm no expert, but I've spent some amount of time trying to find the right pair of jeans and learning the confusing industry terminology. There are a number of things to consider when making your purchase, so I'm going to break them down. #1 and #2 are essential, but the rest you can skip if you're in a hurry/don't care.
The first choice in jeans is your fit. Fit in jeans lingo has a specific meaning; the fit will basically determine how tight your jeans will be on your thighs and calves. For men, the names for the cut usually go from Skinny, to Slim, to Straight, to Classic (Regular), to Relaxed. These can range between putting your legs into a straw, to something like putting on a pair of Hammer pants. Levi's alone has 14 different types of fit for men. But if you just want a pair of jeans that'll probably fit and be comfortable, I think you'll probably be comfortable with Straight to Regular. But if things feel tight or too loose in your legs rather than your waist, try out a different fit. Fit can also determine where your jeans fall on your hips, referred to as the "rise". If your jeans feel a little low around your waist, aim for something described as medium or high rise.
2) Waist and inseam (34x30, etc)
This is the most obvious measurement, and you might think it should be standard, but in truth, things are a bit more complicated than that. But as you might guess, these numbers generally represent the size of your waist and length of your leg, in inches. But you don't have to measure these yourself. To start with, use the numbers on your existing jeans as a guide, and buy sizes that are lesser in the waist if you've lost weight. But also bear in mind, jeans can shrink in the wash and stretch as you wear them, so the way they feel in store might not be how they fit in a few months or even after a first wash. As such, you might want to buy jeans from a store with a decent return policy. There's unfortunately not a lot of space in your average dressing room, so it might be difficult to really get a good feel for how your jeans fit at first. But once you find something you think fits well, try to move around as much as you can, and make sure they won't fall down as you walk around or suffocate you. Sit down if there's a seat available. Try to spend at least 10 minutes with them on. Jeans will generally get more comfortable as you wear them, but you still want something that fits right to begin with.
Now, as for the inseam, this number is somewhat less vital and really depends on personal taste. It's honestly not something I'm super confident about, but I'm guessing you won't want to have to worry about turning up the cuffs or anything like that, so get a pair that basically reaches the middle of your sneakers. Anything longer and you might have to cuff them to avoid stepping on them, anything shorter and you might wind up showing your socks all the time. But again, compared to other measurements which can lead to considerable discomfort if not gotten right, it's not really that big of a deal.
3) Other stuff: color, brands
As for color, you'll probably see a lot of different advice online, but just go with what you like, which I'm guessing is roughly mid-blue. Darker washes tend to be dressier and more fashionable, but mid-blue is unassuming and just kinda works.
A lot of jeans are pre-distressed, which means they're pretty much put through a dryer a couple dozen times to give them that beat-up look. Again: personal preference.
Most jeans are pre-shrunk or Sanforized, which means the amount they'll shrink in the wash is limited, and therefore should fit fairly closely after being washed to how they felt in the store. But do not buy shrink-to-fit jeans, which complicate things considerably.
As for different brands: I don't have too much advice in this, it again will probably come down to personal taste and how much you're willing to spend. But do bear in mind that sizing will likely differ from brand to brand, so if you're wearing brand X and want to buy brand Y, the measurements you already have will not be completely reliable. But they're not even completely reliable even within the same brand, so again, just use the measurements as guidelines.
So, that might seem like a lot to take in, but to summarize:
1) Fit: Probably Straight or Regular.
2) Waist x Inseam: Try multiple different waist sizes and spend time to get it right.
3) Other than that, buy what looks good to you.