Make sure that you have inserted each valve into the correct valve casings. Unscrew the top of each valve and check the number on the base of the valve stem. There will be a number from one to three. The first valve will go into the valve casing closest to the mouthpiece. The second valve goes in the middle and sometimes is not marked. The third valve will go in the valve casing that is closest to the bell.
Remove the valves and dip them in warm soapy water. While submerged, use your valve brush to buff the cavities in the valve. Be sure to remove any debris that might be stuck inside the valves. Gently rub down the outside of the valve with a damp towel, dry it off and then leave it on a clean, dry towel to dry for a few minutes. Apply oil to the valves and reinsert the valves into the trumpet.
If positioning the valves and cleaning them didn't solve your problem, clean the entire trumpet. Remove all the slides and submerge the trumpet in the water. Using a snake, work your way through each slide while submerged. Then work through the tubing of the main body of the trumpet. Clean out the valve casings with a valve brush and then rinse the trumpet with clean water. Dry the outside of the trumpet and leave it out in the air for a few hours. Oil and grease the valves and reassemble the instrument.
If you have thoroughly cleaned the trumpet and you see no sign of damage to the outside of the instrument, consider the possibility that it might be your approach to playing causing the problems. Make sure to take in a deep breath into the diaphragm to ensure that you have enough air to play effectively. When applying pressure to the valves, use a straight up-and-down motion to prevent sticking. Often, trumpet players push against the side of the valve, which creates unnecessary friction and can slow the trumpet's response.