First decide on the type of vacuum cleaner you want to buy. Two of the most popular vacuums on the market are; canister vacuums and upright vacuums. An upright vacumm is the the best vacuum to buy for a dorm room as it takes up less space, is easier to maneuver and works well on carpeting.
Consider the size of the dorm room. Upright vacuums come in different sizes. When you buy a vacuum for a dorm room, you will want to purchase a smaller size often called a broom or stick vac. These vacuums are thin and light usually weighing under 12 pounds.
Take a look at the collecting system on the vacuum. Most stick vacuums use a reuseable cup instead of a disposable bag. You can't collect as much dirt but it's cheaper than buying bags and easier for a college student. Buy a vacuum for a dorm room with a dirt cup.
Look at the construction of the vacuum. You can buy a vacuum for a dorm that will serve it's purpose and clean well without spending alot. However, make sure it is sturdy and will not fall apart quickly.
Rechargeable vacuums are handy but they tend to run down quickly and need to be replaced more often than a regular corded vacuum. To buy a vacuum for a dorm that will last several years, purchase a corded vacuum.