It's vital that you read, several times, any directions posted in submission guidelines. Whether you're submitting a manuscript, material for a critique, or a contest entry, you MUST follow all the directions. TO THE LETTER.
Agents, editors, publishers and contest/critique coordinators have very specific reasons for their directions. Many times you have to sit in the person's seat before you see the WHY behind the directions. Here's the main point: The why DOES NOT MATTER.
If the rules seems silly, half-cracked, stupid, oh well. You just have to cope with them. But please, PLEASE, PLLLLEEEAASSEEE follow them.
Let me give you an example:
Some agents, in fact most, state in submission guidelines that they will not accept any material they have to sign to accept. (This means no registered mail, no certified mail, NOTHING THAT REQUIRES A SIGNATURE.)
Let's say you want to submit to an agent who posts this in his submission guidelines. But you think it's a stupid rule. I mean, after all, your manuscript is the best thing he's ever read, right? There's no chance he won't want to represent it. And you need to make sure it gets there safe and sound, right? Why shouldn't the agent make an exception for you since you're going to be the next NYT perennial bestseller?
WRONG. WRONG. WRONG.
Let's say the agent has a post office box. He goes to pick up the mail after hours---keep in mind he's been on the phone with editors, other agents and clients all day, he's had to read queries, maybe look over a client's work for submission--- and he gets a nice little green card that says he has a package he must sign to accept. Since the submission guidelines SPECIFICALLY STATE no signatures, maybe the agent thinks its a special package---a gift from an author, a BIG CHECK, or a knitted scarf from Grandma back in Vermont. So he changes his schedule, makes another trip to the Post Office the following day to pick up the package, waits in line (when he could be reading queries, calling an editor, updating his website), signs in the TWO required places (once on the card and once on the credit card machine), looks at the return address and finds the package is from someone he's never heard of, someone he's never solicited material from, and guess what? HE'S STEAMED. Who wouldn't be?
Did you think of this when you slid the rule into the stupid column? And now that he's really ticked off, do you think he wants to read your stuff? Rush to offer representation? No. No. And no.
This is just one explanation for one rule you probably see quite a bit. All those other rules usually have logical explanations that most of us have never considered. So please, don't shoot yourself in the foot before you ever get out of the gate. Follow the rules. Even if they don't make sense.