You sure can. About 75% of the time a fan will have two directional arrows on the edge of the fan body. If they don't have that, you can always look at it this way;
If you want the fans to blow air towards the rear of the case or out of the case, the open blade side face opposite. If you want a fan in front of the case acting as an intake fan, simple keep the open blade side toward the front of your case. THE SIDE of the fan that has the wiring/4 cross like bracket, 99.99% of the time it blows the air that way. Open blade side 99.99% of the time sucks air.