Andrew asked about writing coverage. Script coverage is a report that includes a synopsis, comments and rating of a script.
I find people that always do a better job at coverage when they understand WHY they're doing it. So, WHY are you writing it? Basically, coverage exists so that more important people don't have to waste their time reading scripts. Instead, they'll read your coverage and know if it's worth them taking a read. At production companies, you'll read scripts to find out if the producers want to become attached, develop the scripts and take them out to try and sell them. At studios, you'll read scripts to find out if the studio wants to buy the script - or you'll read scripts as writing samples from writers to see if they'd be good to adapt or rewrite other projects, or join the staff of a show. At an agency or management company, you'll read scripts to find out if your company wants to represent the writers, or if your current clients will want to become involved (to star, rewrite, or direct). Sometimes you might have to cover books or plays for possible adaptations. The situation will affect what you focus on.
Your synopsis should be an objective breakdown of what happens in the story - you won't give a sense of whether it's good or not. I generally find it easier to read the whole script first and not write the synopsis as I go, because if you do the latter you won't know which events are more important than others and you'll write down everything. It'll take you forever (and be annoying for the people who read your coverage). One the other hand, your synopsis should be long enough to get a sense of the whole movie. In some cases, people will have to get on the phone and talk about the script as if they've read it - just by reading your coverage.
In the comments section, you'll want to comment on things like plot, story, dialogue, concept, commercial appeal, character development, acting roles, character arcs, etc. Is it easy to follow? Does it have satisfying arcs? What shows or movies could you compare it to? Is it original? Is it derivative? Are the characters interesting? Likable? Are they castable - would actors want to play them? Is it predictable? What is the tone like?
I've only really done feature coverage but in the TV world I'd imagine you'll be commenting on the same kinds of things. Additionally, for specs, did the writer nail the world and tone of the show, and the characters' voices? For pilots, can you see where the show is going? Would it sustain a whole series? Are there series conflicts set up in the pilot?
And then you'll generally give it a PASS, CONSIDER or RECOMMEND. Pass means that whomever you're reading for won't need to read it. Consider means you didn't love it, but it's worth them taking a look. Recommend means you like it a whole lot. Some companies also allow you to make a distinction like WEAK CONSIDER or STRONG CONSIDER. A rookie mistake is to like everything you read - but as you read more and more, you'll get more discerning. Of course, you want to be careful not to get so jaded that you hate everything and pass on something that turns out to be a big success somewhere else. Remember that an imperfect script might make a good movie. Seasoned, successful veterans of the business are able to spot potential within these scripts. Bad dialogue can be rewritten. Tones can be changed. Characters can be more deeply developed. As writers we want to try and nail everything - but as a reader, looking for perfection in every aspect of the script isn't always the goal.
In the couple dozen scripts I've covered for the agency, I've passed on most, considered maybe six or seven, and recommended only one. That one is actually now set up at a pretty big actress' company, which makes me feel like I know what I'm talking about.
Nobody writes amazing coverage at first. Talk to people who have done it, and discuss with your supervisor what it is that he or she is looking for. Every company has a different philosophy, and is looking for different things.