Know your openings!
You didn't mention time control, but it doesn't matter, you just may not allow yourself to waste precious time on opening.
Avoid sharp, theoretical lines if you can not memorize them fully.
I usually avoid such openings because if you face a novelty/variation you haven't seen so far, there goes precious time on thinking for a move that will "keep me in the game", and usually you will end up caught in the endless loop of searching the only move that "keeps you in the game".
Take solid lines that give equal chances, do not worry about possibility of a draw. Since this is blitz, people make mistakes/blunder more often, and do not forget that time trouble is a huge factor here.
Your job is to play the opening as fast as you can, without any mistake, so you can get a playable middle game with equal chances and concrete and simple play/counterplay.
In the middle game, simplify a little, so you can protect yourself from sudden tactical blasts and to reduce the calculation (believe me, in blitz, time flies and before you know it, you are in the time trouble ), but keep enough peaces on board so you can complicate if you feel you can win ( exchanging 2 minor pieces would suffice since it greatly simplifies, but still leaves you with good chances to complicate if you really need a win).
BE VERY CAREFUL WHEN EXCHANGING PIECES!!!
In blitz, people often offer exchanges to simplify, so always assess the resulting position that will arise after the exchange.
This method will give you the best results-offer them unfavorable exchange ( e.g. offer your bad bishop for their good one ). You will be surprised how many people make wrong exchanges!
Practice tactical blows on the real games, NOT on the artificial studies/problems and try to find those examples related to the openings you play.This will additionally protect you from sudden blows.
And again, prepare openings thoroughly! ( I just can't emphasize this enough ). You will want to use your time only for calculation, not on the opening.
EDIT ( updated on December, 20th 2013 ):
About the clock:
Do not forget to press it when you play the move-most beginners/those who are not used to clock, forget it.
What will happen is this:
After you make the move, without activating the opponents clock, he/she will just stare at the board like an idiot, doing nothing.
You will start wondering what is going on-are you winning so he/she thinks how to save the game, or did you play something utterly stupid so your opponent calculates the refutation?
Neither is happening! Your opponent saw you not pressing the clock, so patiently waits for your time to expire, in order to claim win due to you exceeding the time limit.
Yeah I know...there are all kind of people out there :)
As for notation, as soon as you play your move, press your clock first, and then write down the move.
Why? Because if you play blitz at more than 5 minutes each, you do not have to write down moves if you have less than 5 minutes ( double check this, since it was a long time I have played blitz, and this information was told to me by a friend ), and your time is always the highest priority in blitz, you can always write down the move after the game.
If I recall correctly, in 5 minute blitz you do not have to write down moves ( again, double check this ).
Hopefully this will help you.