Make sure your foot is set flat against the foot-board when using the heel-down technique.
The closer your toe is towards the accelerator chain the better control you will have. Keeping your heel down, lift the front of your foot to release the bass drum pedal gently ensuring the bass drum mallet doesn’t swing too far back towards your shin. Feel the resistance, pushing the pedal down gently, gradually and releasing to develop your foot control.
Remember if you let the bass drum beater pedal rebound from the bass drum head with each kick you get what is considered the best sound, known as ‘not burying the bass.’ Experiment with allowing the bass pedal bury bass combinations but it is best to not rely upon this entirely. Listen to both tones to hear the difference.
Aim to get an even sound with your foot pedal pressing down and up in a controlled tapping. Use slow, single kicks before adding double kicks and triplet kicks with accented rhythms.
If you want to do fast drumming, heavy rock or metal, use heel-up technique with more weight behind the foot. Have your heel up and press the weight of your whole foot coming down on the front of the pedal. The weight of your leg will be behind it and it will be much louder.
Start slowly and build up gradually, practising daily until your bass drum pedalling becomes fluent.