Keywords: developer
It turns out I've listed 10, but that sounds too cliche. ;)

I've been meaning to write this for a while because I keep repeating myself when giving feedback to various games. I've also included some issues I've come across in my own work.

For more tips, try Dream Makers. There, something like this would probably get the full treatment with pretty pictures. Developer logs are less demanding. Care to submit one?

  • Never center the text of your instructions.

    Lines that begin at different positions across a page are difficult to read.
  • Avoid walls of text.

    Readers need to be able to jump to specific sections in a hurry. Break your text up. Pictures are helpful. Different text styles are a must. Try section headers and contrasting colors.
  • Remove unused status bars.

    If you have information that can only be displayed by hovering over the map, then go ahead and use the status bar. However, if your graphics are so bad that people can't tell what something is by looking at it then you have bigger problems. Hovering to read "floor", "wall" or "background" is pointless.
  • Remove unused/underused menus.

    Menus take up a row of the screen no matter how many options are available. If you only have a few items in the upper-left corner, it's not worth the space. Try using buttons instead.

    Remember that the quit command is already available by closing the window. Meanwhile, Dream Seeker options can be found by advanced users who right-click the window in the taskbar. Players are more likely to require game-specific options.
  • The left sides of chat input and output should line up. Input should be displayed immediately below output.

    This allows players to view incoming dialogue while typing. It also offers quick feedback after the input is entered. Other setups are wrong!
  • Hide controls until they are needed.

    Only display the tools required to play a game to those currently participating. Those just logging in don't need a bunch of confusing options. Spectators don't need to see the tools players do.
  • Make labels larger than necessary to fit text.

    The font size of a label can be adjusted. A specific font can even be suggested. However, there is a strong chance that what is displayed on a player's computer will be different from what the developer has seen. (Also remember that certain fonts have distribution clauses in their licensing.)
  • Avoid spamming output controls whenever possible.

    Most actions can be displayed on the map. If dice rolls count, place the dice on the map. If player pieces move randomly, their positions on the map should tell players all they need. If players take turns and are not identified by avatars on the map, just slap the name of the current player in a label. If players can't affect the past, don't bother displaying outdated information.
  • Avoid using too many colors.

    If everything is a different color, everything looks important. Players won't know where to focus their attention.
  • If using a skin texture, try one with low contrasting colors.

    This makes it easier to choose a contrasting text color that will show up on top of the texture. It also avoids the need to divide a skin with opaque labels.
I'm inclined to agree with everything said here.
I agree with all of them, specially avoiding too many colors and walls of text. Ugh, hate those.
Something which isn't taken into account is centering the player icon in the middle of the screen. Depending on the view size, I often see the player above or to the left of the map center.

This can be easily fixed by adjusting the client pixel offset.