Here is a simple checklist you can use if you are having trouble with noisy EMG signals:
Are the electrodes "fresh"?
Stick on electrodes have a gel component that can dry out over time, ensure that the gel component has not dried out.
Clean the skin thoroughly
Abrade/exfoliate the skin and clean the skin using an alcohol wipe before placing the electrodes on the skin. This will help to reduce signal impedance.
Make sure that the stick on electrodes aren't touching
Movement artefacts and noise can be introduced if the stick on electrodes are touching or overlapping. This is only relevant if you are using two separate stick on electrodes per sensor, electrodes with two attachment points are available.
Check that the noise isn't from electrode cables or sensor movement
Movement artefacts are a common source of noise, particularly when recording movements. To reduce this it is important to securely attach the sensor body to your subject and be mindful of electrode wire placement. Try to avoid having overly taught or slack electrode wires and ensure that they aren't kinked or crossed.
Do your signals keep dropping? We have a guide here that may help solve your issue.