Realize that the field is very competitive. Understand that you might get out of school with your shiny new ID degree and not be very employable.
Learn to draw better than most of your classmates. Being competent won't help you much, there's too many people that are like that for you to stand out in this field.
Learn form development and understand what makes a design beautiful and attractive to people.
Learn to use Alias, Solidworks, and Adobe CS (and maybe Rhino, form'z and 3D Studio Max) better than most of your classmates.
Start getting internships your FIRST year, even if its only taking the trash out.
Think about and learn what makes some products more successful than others.
I have a whole section for modelmaking skills I wish I knew when I started:
Buy your own toolbox and stock it with your own supplies. Don't depend on shop tools. They suck.
sandpaper 50, 100, 800, 1000 & 5000 grit.
ruler for measurement
ruler for cutting
dremel tool and/or various files
or spray gun
3M Super 77
Weld-On + application brushes (for joining acylic and some plastics)
Utility knife + extra blades
X-acto + extra blades
Wood filler (for sealing foam)
Bondo (for fixing errors in models)
Epoxy (for joining wood and almost everything but plastic)
Give yourself 1 1/2 times as much time to finish your model than you think you'll need.
Watch your fingers when using an x-acto. I've seen LOTS of injuries from using too dull blades, so replace yours as soon as it starts binding.
Realize that even after you finish carving the model, you could easily spend 4-6 hours sealing and painting it, so prepare accordingly.
Have a very clear plan of how to make your model before you begin, and have all your materials + extra with you before you start. Don't make it up as you go along. If you want to just make a sketch model to think while you work, use some lighter grade foam. But for the most part have a very clear idea of what you want to do.
Use a dremel tool to make fine details in models. Easy does it. Don't hold your model in one hand and dremel with the other. Secure it to the table somehow (not too hard or you could damage the foam, though)
Buy your own googles and wear them everytime you are in the model shop.
Wear the best respirator you can find when making models.
Before using any power tool, think if there is any way that doing what you are about to do could hurt you or anyone else.
Super 77 glues foam stronger than steel if you spray both sides and give it about 3 minutes before you put them together, then press both sides together for about 5-10 minutes.
Use the most dense foam you can find to make models. Or renshape. Less dense foam snaps.
Don't make models out of pink or blue insulation foam unless you absolutely have to. Heavy yellow urethane or renshape is the way to go.
Have some bondo ready to fix your foam : ) You will make some mistakes.
Cut a foam cube the same dimensions as your design, then glue Illustrator templates onto the side, top and front of the model. Cutting along those with the bandsaw should give you a rough outline of what your model should look like. Unless you are very skilled, eyeballing it will just result in a lopsided model that you'll make 25% smaller trying to get evened out. Use templates!
Use a sanding block or one of those tiny hand sanders, not sandpaper and your fingers. Use a very rough grade for removing material, and have a lot of ligher grades for sanding primer later. Much more consistent and smooth.
Use a spray gun for making models, not rattle cans. If you MUST use rattle cans, use automotive grade spray paint, like Dupli Color or Plasti-Cote. Never mix brands of primer and paint, and never mix types of paint. Throw that can of Kylon or Rust-O-leum in the garbage where it belongs.
Avoid all nighters in the shop like an STD. Staying up all night doing creative sketching and eating pizza with your friends is NOT the same as desperately trying to get a model together before an 8 am critique. Avoid using powersaws when very tired, distracted, or sick. You need your fingers.
Use wood filller, not spackle, to seal your model before painting.
Paint using very light coats. 3-5 coats should do it.
Wet sand your primer using progressively finer grades of automotive sandpaper. Lightly. Make it smooth as glass before you apply your final color.
Always spray a test piece of foam beside your model so you can touch that instead of the model to see if it's dry. Much faster than sanding and starting over again.
Realize you have to make about 4-12 models before you figure out the fastest and best way to make them. Don't be afraid to ask upperclassmen, instructors, or the person running the shop for advice. Spending five minutes consulting with someone could save you 5 hours fixing a model down the line.
When your model is finished, painted, dry, and beautiful, take it to the photo booth and take several well lit, high res, photos of it IMMEDIATELY. Models get damaged, dropped, etc. very easily so document it well. Better to do this now than have to go back in a year a re-shoot it later when you realize the photo you have for your portfolio is either lousy or non-existant.