You get more pay by flying specials, excessive customer delays, or by picking up an extra line somehwere. Some examples:
1. A line pilot flys a special in addition to his normal run. In that event the pilot is paid at a rate of 1.5 units x the block time or 1 x the time, whichever is greater. A unit is basically an hour of pay. That could be a company sold flight or as simple as a reposition.
2. If you have to wait 2 hours past your block time for a customer delay you get 1 unit per hour delay after that.
3. If you have a run that terminates Friday morning, and you pick up another out and back that night, you get paid the other run's 8 units.
Additionally, you will be paid for travel time, per diem if other than your run for more than 24 hours, and reserves can make extra units by exceeding a 12 hour duty day or in some cases handling the freight. Some of the extra pay is handled differently by different bases. It's all one company, but each base is kinda run like it's own franchise. Hope that helps.