How to install easyplay:
1. Download and open the zip file (google 'Winzip' and download the free version if you don't have it).
2. Extract the files to a folder outside your d2 folder (desktop works great). Click the 'extract' button, select 'all files', then find the folder you want to install easyplay to.
3. READ the readme.txt, AND READ/edit the config file (in the easyplay folder).
4. Start d2, log in, go into a chat channel, open your easyplay folder, double click easyload.exe.
5. Attempt to join a game. Diablo 2 should exit. In your easyplay folder, there should now be a file called 'FAILED_MODSIGS.txt'. Open this folder up, copy the 64 digit number. (CHECK THIS WEBSITE FIRST to see if there has been a recent warden update, and look around to see if easyplay is still safe. If it is, go on to step 6. If it's not, wait till the next EP update).
6. Open your MODSIGS.txt file. On a new line, below the 64 digit number that's already there (the so-called constant modsig), paste in the number you copied from FAILED_MODSIGS.txt.
7. Go back to step 4. You might be able to join a game, you might not. If diablo 2 exits when you try to join a game again, go on to step numbers 5/6.
8. Currently, you should get 2-3 modsigs (the 64 digit number is a modsig). If you have more, check this website to see what's up.
9. Go into a channel, load up EP, go into the game. Hit tab, and you're ready to play d2 a whole lot easier.

How do I bring up the map? Hit the 'tab' key when you're in the game. (Thanks MoreTea)
Can I overwrite my modsigs.txt file with my old one? Yes, until there is a warden update. For now though, you can.
Make sure you are running d2 in a window, more info here.

General Solutions:
Have any problem with easyplay not loading, not loading correctly, something like this?

1. Try using d2loader, get it here.
2. Re-install EasyPlay (make sure that you're using the latest version).
3. Read the 'readme.txt' file that comes in your easyplay folder.
4. Read through the config file that comes in your easyplay folder, make changes where necessary.
5. Try to rename the d2loader in your d2 folder to d2loader and not d2loader-1.11b. (Thanks Senkin for this one)
6. Thanks Senkin for this one- A solution for some people who use d2loader is to add -sleepy to the end of the Target line (right click your d2 shortcut, click properties, look for 'Target line') to ensure it doesn't lag you as much.

Windows 2000 users have reported problems with using easyplay. EasyPlay 2.0b is NOT compatible with Windows 2000. Update to Windows XP to use EasyPlay 2.0b, and get the latest Windows updates (service pack 2) for optimum performance.

There have also been reports of EP not working with WindowsXP with service pack 1. Solution? Update to service pack 2 (sp2). It's free, get it here- http://go.microsoft.com/?linkid=3646727 (thanks Haqzombie for the link), or use Senkin's link 3 posts down.

Linux users cannot use easyplay (or at least not without anti-detection), as the anti-detection is based on things that are in Windows and not Linux (Windows 'emulator' type programs in Linux will NOT make easyplay work as far as I know).

From Netter:
There have been reports of loading difficulties when usinig certain mods (such as RGX Mod).

My advice would be to completely uninstall the mod, or install d2 to another location, and use easyplay from the clean install.

Where is the fullbright (or full light radius) hotkey? There is no fullbright/full light radius in EP or EP gold (yet). You can download CrapHack if you want full light radius.

I'm lagging like crazy and I'm using EP. What's wrong?
EP will slow you down a little, but it won't lag you to a very noticeable degree (unless you have a slow computer). Most likely just bnet lag (happens often because of people duping by lagging the server). Wait 10-20 minutes and try again. If it only lags when you use EP, reinstall EP or try the other methods here.

Thanks TheoryOnAngels for this part:
If you have an older/slower computer, the amount of icons showing up on the map from the monsters can make you lag (although if you're using the auto-teleport, you can just turn of the map after you start teleporting.)

Thanks Senkin for this:
Lowering the video quality to low also helps by 200+ ping.

Sometimes I'm playing in a game, and all of a sudden it quits the game and I'm back in a channel. What's the deal?
Most likely it was the 'chicken' feature. If your health goes down below a certain %, you exit the game. To change this feature, you can go into the config.ini file and either turn off chicken, set chicken to make a tp and go back to town instead of exiting the game, or change the amount of life left before you chicken.

"Your connection has been temporarily restricted from this realm. Please try again later." AM I BANNED? No. This is a TEMPORARY restriction (Same as a realm down, pre-1.11). Try logging in in half an hour. If you still see the message, wait an hour. If you still see the message wait a few more hours. If it doesn't go away after 2 days, contact b.net.

I get [insert error here]. What's wrong? Try running d2 in a window, and don't use -ns. More info here