I've repaired my dryer for years. Most of these replies are right on for a starting point - check out the air exhaust hose and filters to clear any plugs. If you can get to it, turn on the empty dryer and go outside to where the exhaust vent is. The flow of air should be substantial, and pretty warm. Sometimes the end of the vent is closed with a flap, or several small flaps, to keep out rain, etc when not blowing. Make sure those flaps are moving freely so they open well when the dryer is running. And if you can get the flap(s) off or at least open, you may be able to reach in and clear out any lint at the end of the vent.
Inside with the dryer off, take a close look at the flex hose from dryer to vent. As many have said, check to be sure it is not kinked or squashed. Usually it is connected with simple ring clamps tightened by screws. You can loosen the screws, pull the flex hose off the duct pipe, and get access to cleaning out the hose and ducts in case they are clogged. Re-assemble and tighten the clamp screws.
Two types of problems can kill the heating element. One is when it breaks or "burns out". In that case there will be no heat at all in the dryer. If you feel the vent ducting or flex hose, it never heats up no matter how long the dryer runs. But it still will run! The other is when it breaks and then manages to drop down to where the broken end shorts out to the frame. As long as the dryer is properly grounded, the unit will still run AND it will generate some heat, just not enough. Meanwhile you will not get a shock from it if it's got a good electrical ground, so you may not notice the problem. In this case you have some heat in the vent ducting, but it's hard to tell whether it is enough or not. So here's a test for this condition. Usually when the dryer is running properly the heating coil gets hot enough to glow bright orange. Now, most have the heater well protected and you can't see it directly. But if you get it running and warmed up for a couple minutes, then open the front door and look in right away, you can see the orange glow through some holes or gridwork near the back of the big drum. It will fade out in 5 to 10 seconds, because opening the door shuts it all off. You also can reach in and feel the gridwork at the back with your hand - carefully! If the dryer's heater is operating completely normally, you should see the orange glow when you first open the door, and the hand test will show uou it is quite hot back there. If you see no glow but you can feel some warmth at the back, probably the heater coil has broken and shorted out to the frame. If you get no glow AND no heat, the coil is dead.
If your checking says the heater coil is broken and needs replacing, you can fix it yourself if you are a really handy home electrical repair person. Otherwise, call a service tech and grab your wallet.
OH, one more cheap thing to check. A dryer works on a split 110v / 220v supply for the heater, but the motor runs on only one side of that. So it is possible to blow the fuse only on the side that does NOT supply the motor. In that case the motor will run normally, but there's no heat. So, check your fuse panel and look for a blown fuse on the dryer supply. Or, if you have a breaker, take a close look at it and maybe deliberately shut it off, then back on to reset, just in case. Then try the dryer again. A related possibility is for one electrical connection to be broken or loose. Could give you the same effect. but that's more of a problem for electrical troubleshooting inside the dryer or wiring boxes, and I suspect that's not in your of tricks.