There are two main methods - using an electrostatically charged brush, which picks up the dust particles by attraction, or using a sensor swab with a cleaning fluid (pure isopropyl alcohol or equivalent).
I use the brush now, as it's less risky for the sensor. I use a flat artists 3/8th inch Taklon white fibre brush. The specially marketed ones are *much* more expensive! Test the brush first by gently brushing a clean multicoated filter or lens, and look for small streaks under a strong light. No streaks - OK, otherwise you will have to wash the brush carefully in detergent first to get the grease off. You should never touch the brush fibres with bare fingers.
You can charge up the brush by blowing air at it, either from a can, or using a rocket blower. I use about 10 puffs, with the nozzle no more than half an inch from the brush.
Now, put the R-D1 on the B setting on the shutter dial, and open and, if you have a locking cable release (recommended!) lock the shutter open. You can now see the sensor when the lens is removed. Under a bright light (I like to use an LED torch) you will see the tiny specks of dust. I find that if I gently touch the dust specks with a corner of the brush, they will just lift off. A badly dirty sensor may need actually wiping with the brush, but I would avoid that if possible. If the sensor is really grotty, you may have to invest in a sensor swab for the initial cleaning (check out Copperhill in Google).
Anyway, that's more or less what works for me - others will have their favourite methods which will vary.
cheers
Phil