I don't think I've seen this addressed before. They always say, "Pay yourself first ", but that's hard to do if you are on commission. I was for the majority of my career. Here's what worked for me. Some would argue that it's inefficient,, but those people probably never experienced wildly fluctuating paychecks.
I. Set up automatic withdrawal into your 401k or equivalent. Typically, I "only" saved 10% here.
2. Save enough in your checking account until you have a cash cushion. The goal is to build it up enough so you can always be living on last month's money. Better still, the month before that.
3. Use checking account as an accumulator. Once it gets over your designated cushion amount (which for me was 2-3 month's expenses) sweep the excess into savings until you have an EF fat enough to let you sleep at night.
4. Once the EF gets to where you want it, sweep every bit of excess into investments. Repeat, repeat, repeat.
5. Instead of a traditional budget, focus on keeping spending as low as possible and track every penny. Mrs. Frugalwoods' 30-Day Budget Challenge is a very effective method. You can start it any time.
6. Pay attention to income tax withholdings. Because paychecks typically peak and valley, "peak" checks can have too much taken out. The IRS only requires you withhold approximately you owed the previous year. (Look it up, I am not a CPA.) Adjust accordingly and save/invest the rest. Don't wait for a huge tax return.
7. Challenge yourself to tuck away random amounts of money such as any commission over X amount, bonuses, windfalls, etc.
8. If you are reimbursed for mileage or other expenses, try to cash flow them and bank your reimbursement checks.
9. If your job includes perks like a company car or paid cell phone, try to save the equivalent value each month.
10. Don't obsess about your overall savings rate, as many people do on this site. Watching your account balances grow and calculating the percentage saved at periodic intervals is also quite effective.
All of these tricks got me to FIRE on a sub-100k income in a HCOLA, so I know this strategy works. It certainly takes away a good deal of the stress of earning straight commission.