Checking the oil screen
You should periodically pull the oil screen, which is under the smaller round cover just behind the oil filter on the bottom of the motor. Remove the 5 bolts holding the cover on (8mm socket), and remove it. If the cover is very stiff to remove (and most are), tap it gently sideways with a rubber or plastic mallet once the bolts are removed. The screen is held in by the rubber bushing around the edges - you should be able to gently pull it out with your finger. Oil flows through it from the top, so you MUST remove the screen to clean the top side. Be aware that you may get "some" to "a good amount" of oil dripping out when the cover comes off.
Picture of the oil screen cover (lower left corner of photo). Two of the five mounting bolts (the longest two) are circled in blue.
As usual, try to keep your parts organized while you take them off, but if you get confused, just remember that the longer two bolts correspond to the two circled in blue in the photo.
It's not completely necessary to pull the screen, but you'd be surprised how many big chunks of stuff are in there. On Duke's rally bike there was some trash in the engine before it was rebuilt. So, to be sure he got it all out, the screen was checked at every oil change after the rebuild. There was less trash in it with each oil change, but if it hadn't been cleaned the screen would have probably been 60-80% clogged. At the 20,000 mile oil change there were only a couple small pieces in the screen, so it probably won't need to be checked again for a while.
The composite picture on the left shows a bike that had 8800 miles on it. The goop is most likely gasket sealant from when the two halves of the engine case were assembled. The excess has to go somewhere. The stuff that goes to the inside of the engine sometimes falls off into the oil.
The right photo is of a bike with 32,000 miles. The owner (and, most likely, the previous owner) didn't know about the screen until a friend showed him. Stuff caught in this one (instead of circulating back through the engine) was a combination of grit, gasket forming material, and a few silver metal shavings.
In a new motor there will likely be less trash floating around, so it's recommended to check the screen at the second or third oil change, then every couple oil changes after that, until there's no new trash in the screen.
As far as actual cleaning of the screen goes, you can pretty much just wipe the screen clean with a rag. If you do need to spray it, WD-40 works fine. Just remove, clean, and replace. There are no gaskets to worry about for the actual screen; however, the cover has a paper gasket, which could tear. Having one on hand before you remove the cover is a good idea.
Pay careful attention to torque. Since these bolts aren't mentioned in the torque values guide, you have to use the generic value for bolts with a 6mm thread, which is 60 in-lbs. Bolts have been known to shear off when using the values for the oil drain bolt (170 in-lbs), or the generic value for 8mm threads (144 in-lbs). The bolt head is 8mm, but the threads are 6mm. So, 60 in-lbs it is.