As you know the object of magic is to reduce your oppenent down to zero life. All good deck makers know that the faster you reduce your opponet down to zero the better the deck. Speed plays a crutial part in the success of your deck. There are many ways of making your deck faster and they are as follows.
Try to have all of your decks 60 cards or as close as possible. That way you have a better chance of drawing cards you need. This is good for when you absolutly need a card to win and by doing this you would probably get a card that you need rather than just some stupid spell.
Take all unnessary cards out of your deck. This will help you get down to 60 cards and will help you follow you deck's themes. This also helps you get the cards you need for playing your deck. This way you get cards to help you that you need. Also add in the most efficient cards into your deck. For example if you are playing a burn deck, you would add in a Lightning Bolt rather than a Searing Touch.
Another key thing to remeber when making a deck is to add the right amount of land. If you do not add the right amount you could end up getting to much land and not enough spells which could end up with you losing the game. Or you could either get the opposite if you add to little land you could get to little land and end up not able to play any spells at all.
Keep to your decks theme. You don't have to stick to it like glue but try to stay close to your theme. What I mean is if you have a sliver deck you can put in spells to help like a Giant Growth or something but don't put Goblins and things like that in.
When playing a deck strategy can help you win. You must decide the right time to play a card or it could cost you the game. You must know when to attack your opponent and when to keep creatures to block. All these concepts an either win you the game or lose it for you.
One of the most important things in the strategy of magic is to decide when to attack. One thing to consider when deciding to attack is to think about your blockers. For instance if you only had a 1/1 you wouldn't want to attack with a it just because your opponents Scaled Wurm is tapped and it can get through without being blocked. You would rather keep it to block the Scaled Wurm so you wouldn't take the damage. But you would attack if you had other blockers or it would kill your opponent. Another thing to consider when attacking is if you would lose any creatures. Even if you would be able to get lets say 5 damage through and kill 4 of his creatures, all of your creatures might be dead.
Another good habit to get into is to attack before you play any spells. This way your opponent doesn't know what you are going to do that turn which gives you an advantage and you have all of you mana left so you can play instants like Giant Growth.
One little trick I like to use is to play instants at the end of my opponents turn. This is good because it leaves me mana to use against my opponent. For instance you could use this in a Prodigal Sorcerer Deck, or a Counterspell Deck. In a Counterspell Deck you would play instants that would let you draw cards at the end of your opponents turn. In a Prodigal Sorcerer Deck you would wait till the end of your oppoents turn to tap them to deal damage.