Be flexible and fun! Let the players and GM invent aspects at the planning stage of a mission. We were on a secret mission to a Maharajah's palace and while brainstorming our plan we came up with Aspects of 'Monsoon Season', 'Old Codgers' (ex army veterans colony nearby), and all sorts of other stuff that were of benefit to us or of benefit to the opposition.
Make Aspects matter. One of the low points of the first GM's Diaspora game was spending THREE aspects whilst trying to get info out of the Bad Guy and learning precisely nothing.
Make failure interesting. The second GM seemed to be using the FATE rules in a way that even if we failed rolls, we still achieved stuff. So we've found the map we wanted, but the guards are onto us.
Don't make the dice roll difficulties too high. That is a bad habit of the first GM in many systems (Dr Who, Leverage and Fate). In Fate it was particularly noticeable, as the dice will give you a negative result as often as they give you a positive one.
EDITED TO ADD: Oh yes, and make combat/initiative order have some sort of common sense. My character's declaration of "Oh, frak it! I knee him in the balls!" should have my character acting FIRST, even if I then miss or the victim then dodges. The first GM's interpretation of the initiative rules were:
1) I declare I'm kneeing Tom in the balls.
2) Dick hits Harry, because, y'know, Dick has the highest initiative.
3) Tom hits me.
4) Harry hits Dick.
5) Finally, I get to try and do the kneeing which everyone else apparently used psychic powers to anticipate!