Making the weapon line in a color guard is a huge achievement. Spinning a sabre correctly takes technique, strength, precision and timing. You will probably have to practice quite a bit on your own before you will be ready to try out for the sabre line in your color guard program.
Tape the sabre correctly. This is an important first step, because if your tapes are wrong, then your spins will be wrong. There are two tapes on the blade: the spot tape and the catch tape (also called the cheater tape). The spot tape should be black, and is located 1/3 of the way down the blade, from the hilt. The catch tape should be white, and it is located 1/3 of the way in from the tip. If you have a chrome sabre, you will also want to put a long strip of white along the entire top of the blade. You can buy special color guard tape, but electrical/PVC tape works just as well.
Start at right flat. Sabre is parallel to the ground. The hilt should be on your left side, with your left hand resting comfortably on top of it. Your right hand should be palm up under the blade. Your right thumb should be pressed along the back of the blade, at the catch tape.
Subdivide the 5-6-7-8 before the first count of spins, saying "Down Up" on the last two eighth notes, then saying "Down" again to denote the first actual spin. It should sound like this, "Da Da, Da Da, Da Da, Down Up, Down." Practice the subdivision a few times before moving on to the next step.
Release the hilt with your left hand so that the hilt travels counterclockwise into the down position on count 8 of the subdivision (when you are saying "Down"). The sabre should be straight up and down, thumb at the catch tape. Your left hand should just drop to your side, nice and relaxed, and stay there until you finished the spins.
Let go of the blade with your right hand as it rotates counterclockwise around your palm. The hilt should be up when you are saying "Up" (the "and" count between 8 and 1). Your hand will not be touching the sabre on the "and" counts-the sabre will actually have just a little air under it. The "and" counts are mid-flip between the whole counts where the hilt is down.
Catch the sabre straight up and down, as you say "Down" again. The hilt is down, right thumb at the catch tape, pressed against the blade. This is count 1.
Continue the counterclockwise spinning motion. Release your right hand from the blade for the "and" counts (as you did in Step 5). Re-catch in the same spot on the blade, with the sabre straight up and down (as you did in Step 6). This release, pinch, release, pinch technique will go on for all of the counts.
Stop the sabre from spinning by simply bring your left hand up into position, palm up, fingers open. Right hand will catch overhand at the catch tape. You won't change the velocity of the sabre or anything else your right hand is doing. The sabre stops moving by suddenly meeting your left palm (so the sabre is only rotating 3/4 of a turn instead of a full turn). Some color guard instructors prefer that you do a toss at the end to stop spinning, where the sabre rotates one 3/4 turn.
Switch sides and repeat on the left, starting at left flat (sabre parallel to the ground; hilt to the right with right hand resting overhand above the handle; left hand palm up under the blade, left thumb pressed along the back of the blade, thumb on the catch tape). The terms right and left will obviously be reversed in the instructions above if you are applying them to left-handed spins.