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.