Toilet Bowl Drains Slowly

The bowl or drain is clogged or blocked

Plunger
First, prepare the floor around the toilet should water overflow or splash out. If the bowl is overflowing or filled to the rim you will need to bail it out. Use rubber gloves, a bucket and a small container to empty about half of the water from the bowl.
If the bowl is empty fill it to half full with water.
Place a plunger flush over the drain opening in the bottom of the toilet. Quickly pump the plunger about a dozen times, then remove it with a quick motion. If the blockage is dislodged the water should rush away. If not, repeat the process as necessary.
Auger
If a plunger does not clear the toilet an auger will likely do the trick. Be careful not to scratch the porcelain in the bowl when inserting the coil into the drain. Once the auger is fed into the drain turn it clockwise until you feel resistance. Then turn it counterclockwise. Repeat this process to clear the clog, then remove the auger from the drain. If the drain is not fully cleared try using the plunger again and then repeat with the auger if necessary.
Remove the toilet
If you are still not able to clear the toilet you may need to remove the toilet to remove the blockage from below.

Float ball is too low or adjust water-intake assembly

Reposition the Float Ball
If the float ball is too low the toilet may not flush completely and you may need to adjust the float ball back up slightly to get more water in the tank. You can simply bend the float arm up slightly to keep the water about 1 inch below the top of the overflow pipe. Flush the toilet to a make sure it enough water is getting into the bowl.
If it also possible that the float ball is damaged or rubbing against the side of the tank. If it is rubbing the tank, gently bend it toward the center of the tank. If the float ball is damaged, it will not rise enough to close the ball cock. The float ball can be screwed off of the float arm counter clockwise. You may need to use pliers to grasp the float arm. When placing the new float ball on the arm, apply petroleum jelly or plumbers tape to the threads.
Adjust the Water-Intake Assembly
Your toilet may have a water-intake assembly instead of a float ball.
To adjust the water level in the bowl so it does not flow into the overflow pipe, pinch the clip attached to the thin metal rod and slide it and the cup down to lower the water level.
If the water level in the tank is too low sliding the water-intake assembly clip and cup up will raise the water level.
Try moving the clip about an inch at a time and flushing the toilet to see the results.

Flush holes are blocked

Clean and clear flush holes
If the flush holes below the bowl rim are blocked the toiled will not drain properly. You can try using toilet bowl cleaner and a brush to clear the holes. If that does not work use a coat hanger to clear the holes and clean the bowl again.