Check that the height of the nozzle has the proper level when starting the print. To check up the height, take a sheet of paper and it should just slide freely between the nozzle and the bed.
Check that the print temperature is correct (often between 185 to 210°C for PLA and 220-235°C for ABS). Also check the heat bed temperature (60°C for le PLA and 110°C for ABS.
Clean up the heat bed with acetone (preferred) or window cleaning liquid to remove any traces of grease.
Change the polyamid tape to renew the print surface . This type of tape is very robust and can be kept for tens of prints. You can keep it until you damage it when removing the part from the print surface.
Apply some hair spray (very strong) on the polyamid tape. This should greatly improve the stickiness of the plate. You may want to try different brands/quality (we tried a lot of different brands/quality already) of hair spray as some sprays wont work and some will work great. The price has often nothing to do with the fact that the hair spray will more likely work, so feel free to experiment and when you feel one brand/quality is good for you just stick to it.