Alright. I am a comparatively new GM, but I have figured out a system that works for me. First, A little background. I was running the pre-made in the back of the Core Rulebook to introduce my party, a bunch of new charachters to my campaign. In that shootout with the two young gang members at the start, one guy took it slightly out of proportion. long, hilarious, infuriating story short, the PDF and the Sisters of Battle were undergoing a deployment around Port Suffering when the mining melta charges they stole went off and took out half the city. They managed to make it up with their inquisitor (they now all wear explosive collars), and they are now trapped in Volg's underhive, with literally millions of mutants hurtling at them. What I am trying to get at here is that I got there by writing out the first few minutes of the adventure (where they are now, what will happen in a few minutes, with a clear goal in mind for the Acolytes. That makes it more fun for me and for the players. I'm looking for opinions, recommendations, horror stories (why oh why did they shoot so-and-so) etc...

I Have done this once or twice and i have one key thing to say: be careful that your players don't truly surprise you! I have had this happen, once i ran a campaign where i had my players go down to a war world and find themselves in an imperial base and have a simple mission branch out from there, well, my players decided to activly attack the obviously chaotic forboding base i had originally placed on the horizion to push them TWARDS the imperial base, needless to say after they were forced back by overpowering gunfire and faced the issue of a long trek back without a vheicle to transport them, (had i been a less experienced GM that could have turned terrible and miserable for everyone) but instead i had them get picked up by a commisar and congradulated...however, the only other key issue to avoid (and if you can avoid this then kudos to you!! i mean it) is the appearance of railroading (my players activly destroy railroad tracks on sight).. if you encounter this problem you have to immediatly amend the issue...no one likes to play with the assumption that your decisions won't affect the outcome. The only other thing to avoid is what i call the CARDBOARD SCENERY, which is where due to lack of planning (usually because my players really surprise me about their plans, such as a psyker on an agriworld investigating cult activity activly joining one of the cults seceretly rather than investigate) causes a rather sadly detail sparse enviorment to surround your players, where you are forced to name the NPC they just met with a random name that you may not remember after 10 minutes, or that you are forced to use simple words like grand and fancy to describe the cathedral the players just entered, the feeling that you just didn't do the set justice. Once again it is very possible to avoid this gracefully, it is just something to keep in mind, sometimes I make a card of general set 'feelings' like creepy, 'magical' and 'pristine', with a list of objects, set pieces or descriptive words just to use for illumination of the setting.

other than that, if this style works well for you, i commend it, i find it works alright, but if you have any idea of where you want the group to go, it is ussually good to make a series of quick notes to cover the most basic of your settings.