Also don't fudge rolls, the players will realise this and then it has the possibility to create a undesirable situation where there is no risk as the players will expect you to always bail them out.
Again, fudging is just a tool, its not inherently evil!
Whether fudging is done at all depends upon the situation...and no, you don't fudge things so that everyone gets away scott free and rides off into the sunset with the princess and the pony every time...
You fudge only when it furthers the storyline or increases the fun of your players.
One of the last 2Ed PCs I designed died from a maxed-out crit from a 2-handed sword on the first swing of the first combat of the campaign. Hours of PC design, a campaign-specific PC history, etc...gone on a fluke roll.
The DM informed me that, had the campaign continued (several of the other players actually had to leave town before the next meeting), the PC would have awakened captured, not dead.
And its not like all of your fudges should be pro-player, either. Sometimes, you fudge in the favor of the NPCs.
I ran a campaign that started by having the party kidnapped by intradimensional sea-raiders...except the dice rolls were consistently going in favor of the party. Their initiatives were high, their to hits and damage were all well above average...they were winning despite being outnumbered 3-1 by NPCs that averaged 2 levels above them.
If I hadn't fudged that battle (by recycling the fighter NPCs), the campaign would have died stillborn.