I'm fond of the SpotTone spotting pens - others dislike them.

Make sure you have excellent light - even, diffused, of good intensity and reliable colour.

Too little is much better than too much.

Tiny spots laid down in a figure 8 pattern fill up an area better than any attempt to lay down larger amounts.

Matte or semi-matte paper is your friend.

And make sure you don't mistake details of the scene for dust and mistakenly spot them out.