write everything honest the first time through - just belt it out and avoid too much re-write.
write what you are really thinking, dont soften your thoughts - if you write in an honest mood for yourself you wont need much editing.
when i start writing like a publisher-potato pansy i go read some william s. burroughs or hemmingway to snap out of it.
someone else can check your grammar, it's more important to have a good story or characters you can sweat with.
some editors will send you proposed changes that will often center around 'plot points'. on things like screenplays they literally count scenes and tell you to develop the character in 'x' way before scene 'y'. it's ridiculous and it's why a lot of work seems the same. the public buys up formulaic slop and publishers know that.
dont go for these changes, you'll get published quicker but you will be putting out millwork and thats negates the achievement of writing.
oh yeah, be sure to mail a copy of your completed script to yourself certified mail before you start shopping publishers etc. there are a lot of unscrupulous people out there and this is a cheap way to establish proof if someone steals it.
avoid writers groups especially on the web - everything they say, they "write" - it gets so that you cant get realistic feedback, its all meant to sound 'writerly'.
see how easy that is?
good luck.
