Storygirl gave some good tips there, but I do have to drop my two cents worth of qualifiers on a couple of them.
First: The adjectives thing: It's a matter of taste. I know I tend to be a little liberal with my adjectives, but to put a cap on them is tricky. Yes, if you're writing a brisk tale in a modern setting, you can sweep the reader along with next to no adjectives. But if you're immersing them in a totally alien world to what we know here on earth, descriptors will be necessary...especially to accomplish the earlier goals of establishing setting and genre.
Second: While I am quick to jump all over being verbs as main verbs in a sentence, advising a writer to reword to find a more active verb, there is a time when you simply must use 
had or 
has, and that's in the past perfect tense. Sometimes you need to refer to an action your character has done in a previous timeframe of the story, and if you don't use past perfect: i.e. "He 
had purchased the armor from a reputable smith in Myslapten and therefore could not understand why it deteriorated so quickly." If you say "He purchased," that noun-verb combination implies that the action takes place in the time frame that is "now occurring" in a story written in past tense. (Which most are.) So, I would say, avoid "He had a cold" as a use of had, but IMHO, it should get a pass if you need to go past-perfect.
Last: (This is actually more of an agreement) Adverbs. Yes, at times an adverb can be a crutch to prop up lazy writing. Better to find a way to make the statement in a way that eliminates as many adverbs as possible. My personal pet peeve: adverbs in dialogue tags. It's so much better to put the bite in your speaker's word choices than it is to say " she said bitingly." (Okay, so that was an especially atrocious example, but I think it therefore amplifies my point. 

 My only qualifier here is that there are times that an adverb is needed. No part of speech is bad in and of itself. It's lazy usage that makes adverbs the villain of the contemporary literary world.
As for other issues I'd say to watch out for: POV is one of the biggies. If you don't have a handle on that concept, read up! (I recommend Orson Scott Card's 
Characters and Viewpoint for starters.) POV errors will kill your manuscript in the eyes of many editors.
Also...passive voice, in the classic sense where the subject is not the thing doing the acting, but rather is acted upon. "The battle 
was fought by the orcs and the men of the southern plains." SOme examples won't be so obvious, but most of the time, you can reword to make the subject active. An occasional interjection of passive voice can add punch, but too much of it makes me close a book, to be honest. 
And last: search for the word "that." You'd be surprised how many times it sneaks into a sentence where it's not needed.
Okay, enough from me. "Blah, blah, blah..." 
