The scoring system used can seem complicated, and sometimes it is depending on the history. The entire process is in section 920 of the Florida Statutes. There, you can find scores for particular crimes, scoresheets used to calculate scores, and other information on the subject.
Essentially, each crime is assigned a value (current and prior), they're added together, and then multiplied by a factor to derive the final score. Sometimes there's a wrinkle, like crimes older than 10 years can be ignored IF the person has not been convicted during the interval.
The result provides a guideline score. A judge can go below the guideline if certain factors are present and made known. They're listed in the section 920.0026 statute: mitigating circumstances. During sentencing, the State can recommend to the judge anything from below guidelines to the max for that crime. In all felony cases, a proper guidelines scoresheet must be created and entered into the court file regardless of the actual sentence imposed.
Check out the statutes here:
It's chapter 921, I think he made a typo. And the forms for the scoresheets are in the criminal procedure rules starting with 3.992 for the current one, and go backward for the older ones down to 3.988. You'll need a lawyer to really help you get it done right, and even then, we fight about what's right in court all the time.