In general, it's a bit normal to have some filament ooze during warm-up. However, if it seems to be an abnormal amount, you may want to consider reducing your target temperature.
Keep in mind that ideal extrusion temperatures are subjective to the source of your filament. Not all filament is of the same material quality and differing degrees of purity. Sometimes, the same filament will be of different quality from the same source. It might be worth dedicating the first bit of each spool to a bar test to determine what the appropriate extrusion temperature should be.
A simple test would be to use the control panel on your machine or use your software (whichever is easiest for you):
- Manually set the extruder to extrude filament
- Stop the extruder
- Clean excess material from nozzle
- Watch for ooze
- Gradually reduce the temperature
- Repeat until the amount of ooze is an appropriate to your liking
Also remember that there will be some left-over material from a previous spool when swapping spools.