Work rules determine how the pay scale gets applied, and how much time off you have. My examples are for the regional level...

Guarantee: The minimum number of flight yours you will get paid every month (or bid period), regardless of how much you fly. Reserve pilots often live on this (which is what I'm doing right now). Varies between 65-80 hours/month. My goal is to either fly as little as possible or as much as possible, but not in between. If I fly 20 hours but get paid for 75, that's not bad! Once you go over the guarantee, you get paid for actual flight time. I don't like to fly 73 and get paid 75 if I could have flown 20 hours and STILL got paid 75. But if I can fly 95 hours, that's a nice chunk of change (20 hours) that I get ABOVE the guarantee.

Min days off are usually 8-12 per month, reserve pilots sometimes have less.

Duty Rig: Pays you a minimum flight pay per hour of duty. 1 for 3 or 1 for 4 is typical. This is important if your company schedules long breaks in your flying day, or if you have a lot of WX or congestion delays at your base. If you don't have a duty rig, that's bad, because not only do you not get paid, but the company has no incentive to not waste your time. You don't want to have a 13 hour day with two :35 minutes legs and only get paid 1:10 for 13 hours of duty...Note: The guarantee still protects you for your monthly min.

Trip Rig: Min pay for the entire time you're away from base. Typically some value less than the duty rig, if you even have one. If you fly to some exotic destination, and have a 30 hour layover you would get paid something while sitting there. I don't think many regionals have this.

Per Diem: Cost of living allowance paid for each hour you are on duty or away from base. If you sit ready reserve for 8 hours at the airport, you get 8 hours per diem. If you go on a 4 day trip, you get paid 4x24 = 56 hours per diem (depending what time you actually depart and return. $1-$2/hour is typical rate. Buying airport food will eat up your per diem.

Block Pay: Do get paid flight time for block-to-block (gate-to-gate) or just for SCHEDULED flying time? BIG difference. Congestion, WX, de-icing can leave you on the ground for HOURS only to fly a :28 minute leg. You want to get paid actual block-to-block.

Commuter Clause: If you plan to commute to work, you need to know if your contract has any provisions that allow you to miss work if get stuck trying to commute through no fault of your own. Some companies don't like commuters. Eagle used to not even allow new hires to jumpseat or non-rev! If your company allows no-questions-asked "personal days", you could use these if you get stuck commuting.

Training pay: Most regionals will either pay you during training OR provide a hotel. It's about a wash either way. If you get nothing during training, I'd suggest you don't take that job.

So, the big things to look for in employer work rules are guarantee and duty rig. Some airlines don't use a calendar month as a bid period, so make sure you convert to compare. Mesa'a 70 hour guarantee doesn't compare well with the typical industry average of 75...until you realize that mesa is on a 28 day bid period...convert that to monthly and mesa gets 76 hours/month.

I think duty rig is the most critical, it encourages the company to minimize your sit time while on duty, so your duty days are shorter (or at least you get PAID to sit on your @ss all afternoon in the COS airport). Also what people don't realize is that if the company can leave you on duty, but only fly you a few hours, you could go six days without hitting 30 hours. Then you only get minimum days off. If the company has incentive to fly you @ss off when you're on duty, you'll hit your weekly 30 limit in just a few days and then get more days off.

If you have an interview or job offer, try to get educated by a pilot who works there about what their rules are and how they are applied.
Mesa has 8 days off (ten for line holders) no duty rig, no trip rig, and pays on average, not actual block times. You get the picture...