'Be careful about tightening for the sake of tightening: Your sentences will look like stumps, and your body of text will read like a first time driver of a stick shift.' ~ possibly, but not necessarily. if you actually do that excercise i suggested, you'll wind up with a nice mix. like i said, sometimes when you combine short sentences you ferret out a few small words in the process.
what spackjock said was really good. when i critique, i'll come across all of these things with enough frequency to think it's part of the process. granted, no one wants a 'white room,' but sometimes people go overboard with description. i know i do. i also used to be really bad about reinforcing what was already there, but all i was really doing was repeating myself in a slightly different way.
pd's advice about writing on paper is a good one, imo. i'm pretty sure it's been proven this produces better writing.
it's hard for me to say how a story 'flows.' for me, what happens has to be given its proper space depending on the importance of what it is. entering a room and opening the window can be said just like that unless it's got some kind of significance, then it could go on for paragraphs. what i can say is that i like a variety of sentences structures. too, there are a dozen ways to indicate who a speaker is without using the 'biff said' dialogue tag at the end.
i'm not sure what 'act of a scene' really means. some folk operate in a very structured way, each scene having a beginning, middle and end, and inside that they work the same structure into their dialogue. it works for some, not so much for others. and even while i *tend* to leave cliffhangers at the end of a chapter, sometimes it's not appropriate.
something else i do, which i'm not quite sure if it works or not (and i do this quite often in a post), is to follow a technique i gleaned from reading professional op-ed pieces and humour articles. it's something they must teach, but i just happened to figure it out on my own, lol. open up the newspaper and find said op-ed or humour article, and you'll find a main idea early on that's expounded upon, then the very last sentence will sum the whole thing up and have a lot of power. (i've noticed this more in humour pieces, so i suggest you start there. it's hard to describe this early in the morning, but it's pretty easy to recognize if you know what you're looking for.)
how do you use description? when you figure that one out, let me know, lol. some things you can allude to, others are implied, some has to be laid out in no uncertain terms. sometimes you need a bit of detail, sometimes not. someone's space in the cubicle farm may not need much, but you're probably not there to establish much of a mood, eh? then again, if you want to mention the personalization of that space in an attempt to resist unsanity, i think it has to serve a purpose. so, i don't think there's any formula to it, really, and it's one of those things you have to study and figure out what way best suits your storytelling method. you're likely to study different methods and cobble together your own way of doing things. it's impossible to say what details will attribute a great mood to a place without knowing specifics (though there are some likely helpful suggestions). some aver three details are all you need, no more, no less (and then slip in a few more through dialogue or character first impressions). some writers absolutely refuse to give up a character description, but i feel that's strongly dependant on the genre and reader expectation.