I keep a spreadsheet that lists all the shops that I have scheduled, plus the ones that I have requested or applied for. I update it as soon as I have accepted a new shop, so I can always see what I have scheduled and when. I also put other important information in there, such as days I'll be out of town or appointments, so I don't forget that I already have something going on at such and such a time and accidently schedule a shop for when I'm supposed to be at the dentist!
The spreadsheet lists each day, which MSC, shop, job ID number, address, fee, bonus (if any), max reimbursement, time frame for shop, and any special notes (like drive-thru, phone shop, must have female guest, do alone, Is the date firm or is there a range of dates for this shop, etc). After the shop, I put in how much I actually spent, mileage for the day (total miles, beginning mileage and ending mileage), and any other expenses related to the shop (parking, tolls, hotels if overnight, etc). When I get paid, I put the date I got paid for each shop and note if the amount was incorrect.
The nice thing about keeping up with the spreadsheet on a daily basis is that it keeps you organized and aware of what shops you have scheduled, and the mileage and payment information is all in one spot when it comes time to do your taxes. Some MSCs give 1099s WITH the reimbursement amount included (which you'll need to take back out as an expense on your taxes) and some don't, so you'll need an easy way to tell. And the search function is awesome! I can go back and see how much I got paid for a certain shop two or three months (or years!) ago and factor that information in when I "make an offer."
I've been shopping for 10 years and my spreadsheet is tweaked a bit almost every year. The top two lines of the spreadsheet have my vehicle mileage on January 1 (you'll need to know for tax purposes); I add the ending mileage on December 31. I just added the "bonus" column a couple years ago because I was curious as to how much "extra" money I was making over the entry level point. I keep thinking about adding a column so I can tell how the job was offered/accepted (just because I would like to know!) - did I accept it via website, text, a phone call, or did I "make an offer?" I'm also thinking of adding "date applied" and "accepted" columns, but I don't "need" that info, I just sometimes wonder how far out I schedule certain jobs or when the jobs are offered to me from month to month.