I keep mineral spirits nearby to clean up drips before they dry if I miss them while fully wet.
I would, with a paint brush.
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Yes, they are hard to remove once dried.
Yes , always keep on the when you are painting , and watch for drips , smooth them out , as soon as possible .
Rose: after they dry, you can sand then off with a fine grit sandpaper... and then use a very light coat of paint over the area.
Here's a post that might help you - https://acrylgiessen.com/en/drying-and-sealing-your-acrylic-pourings/
Not sure about what you are doing, so I will comment generally! Yes I would clean up as I go........Otherwise it requires more work to get it cleaned off. Best wishes!