I would do the following to any new bike. I was dealing with a family illness when I bought my 2001, so Les at LT-Racing "prepped" my bike for me and did the stuff below (and probably more). He is a honda factory trained mechanic/technician and a personal friend.
- Remove the wheels and lube the wheel bearings, they usually come with very little grease from the factory (goes for any bike).
- Disassemble the linkage and use a high quality grease to lube. Glenn (GMP) recommends a good quality waterproof grease. I always forget the brand. Use this same stuff on the wheelbearings.
- Lube the steering head bearings.
- Remove the Swingarm pivot bolt and use either grease or anti-sieze on the bolt to reduce corrosion.
- Check the routing on the wiring and throttle cable. Adjust if necessary. Use safety wire or zip ties to correct any issues (e.g. saftey wire the throttle cable to the top of the carb). For example, my wiring loom went inside the frame and the fuel tank bound on it - Les (my best friend is Les of LTR) re-routed mine outside the frame.
- Check torque on all fasteners and apply a slight dab of anti-sieze to reduce corrosion and ensure correct torque. In key areas - use a thread-locking compound - e.g. sprocket bolts, etc. Note that the torque numbers have been wrong in the manual for many years. Particularly the triple clamp pinch bolts - GMP has produced very nice torque tables for the gasgas (download GMPs from the technical articles on the website here).
- During break-in keep the spokes snug. Spray them down with a mist wd-40 lubricant after every wash to displace moisture and reduce corrosion.
- Check the sprocket bolts during break-in. Note that older gasgas bikes used talon made nuts - these were not flanged and didn't torque well and came loose often. GasGas now uses a flanged nut (so on your 2006, ignore everything I just said).
- Check the jetting and adjust. For my gasgas, I prefered LTRs jetting kit. I find the stock jetting to be very inconsistent off the bottom and there is a very, very rough transition from the bottom to mid.
- Have the suspension revalved for rider weight and terrain.
If I were ever lucky enough to ride an ISDE, I would do most of the above and add the following...
- Mount an LTR chain guide. Some like the stock chain guide. I find it allows the chain to slap around excessively - lots of noise and potential for de-rail. The LTR chain guide is actually a aluminum billet mount that allows you to mount an XR chain guide on the bike. I prefer this chain guide over anything else made for a couple of reasons. It uses a softer rubber on the "chain block" - it cushions and guides the chain well. Being plastic it can take a beating and bounce back. It has a slot that engages the rear sprocket. It cannot bend and become a deraileur. I have never, ever broken one.
- Pick your guards. I would mount a skid plate to protect the frame rails and protect from boulders, etc. "GP radiator braces" are cheap protection for the radiators. The juice clutch slave cylinder is directly in front of the chain - an LTR guard is made to protect it from a de-railed chain from taking it out. I like to run a pipe-guard. In the past I have used a CRD skid plate and Les' (LT-Racing) carbon fiber pipe guard - but the hyde racing stuff looks very interesting to me. The hyde unit is a plastic composite. They have a one piece skid plate/pipe guard.
- I like a slower turn throttle unless riding in open terrain (desert). I run an old honda tlr200 throttle - but Les mounted this on my bike before the cam type throttle tubes became available.
- Replace the stock rim-locks with those made by motion pro.
- Add an LTR mud-guard. This is a plastic piece that blocks mud from entering between the front of the motor and the skid plate. It's cheap and keeps a few pounds of mud from filling up that spot during a ride or race. I think it only costs $20.
- I like running with an LTR power valve cover. It increases bottom end and roll-on throttle response.
- LTR Hi-flo water pump impeller.
- some of the other things already mentioned by others here...
Enjoy your new bike!
jeff