If you have played college ball, you should know that come spring season, you need to be in the best
shape of your life. Triple that. Most milb players do not enjoy spring training, and very happy when it's over.
I went back to read that you were in short season last summer. Short season is usually very laid back, as it is most players first pro experience, the expectations change after your first full season.
Many new draftees come thinking that they will "get in shape" in spring training, you have to be IN shape come spring training. Most new signees get some slack, but now you will be competing to keep your job, not just to get in some at bats or innings. You should be on a conditioning program include lots of cardio and perhaps tossing.
Prepare to be up very early and be at the field for most of the day, maybe one or two days off in 3-4 weeks. Prepare to run, A LOT, make sure you have been preparing for that, well in advance of spring training. Most teams have curfew, but you are so tired you won't want to do anything else but go to sleep anyway.
If you are not prepared by the end of spring training, you will be assigned to extended spring training, more of the same stuff you just did for weeks.
Your organization will be sending you a letter, depending on your position. This letter will outline what their expectations are when you arrive, usually pitchers have to be ready for bull pens about 75%-80% of your velocity.
If you were invited to fall instruction, they usually will tell you what to work on for spring, but not always. Pro ball is about figuring it out for yourself.
If you have any questions, call your drafting scout, they are usually very happy in helping you to succeed.
After all, he is the guy who recommended you for the job.
Have fun.