Initial Setup

After you first unbox your new N810, I suggest the following steps:

Get yourself in a place where you have electricity, wireless 'net access and a Linux or Win32 PC.
Charge the battery. If your battery state-of-charge is under half, you'll need to charge it before you proceed. (You can still play with the device while it charges, just know that you'll lose any changes you make.)
Some few N810s shipped from the factory with the internal memory incorrectly partitioned. Check for and fix this condition if your device is one of those with a problem. Read the technical details under Bug 2940.
Flash the latest OS.
This step will cause the loss of all data on the device. Make backups of anything you want to keep.
If you're using Linux, follow the directions on Maemo.org. If for some reason you're stuck with Win32, see the Nokia Software Update page.
Go through the initial setup. (If you don't want to set up Internet access through a bluetooth phone, you can just cancel out of that bit.)
The default home page is cluttered. Click Home->Select applets and uncheck anything you don't care about. (You can always turn it back on later.) I only have Clock checked on mine.
Set up your 802.11b/g connection by clicking on the WLAN () icon. (If you are behind a proxy server and/or need a static IP, use the Advanced button on the last page of the setup wizard.)
Start Settings->Application manager then from the menu choose Tools->Application catalog.... Select Maemo Extras then Edit. Uncheck Disabled and then OK. Finally, click Close to close the catalogs page.
Still in the Application manager, click Check for updates. There may not be any available. If there are, consider applying them. Note that OS feature updates may disable the Maemo Extras repository; check after upgrading and re-enable if needed.