How are you playing your deck? Casually with friends? Planning on going to events at the local game shop? Do you plan to keep the deck in a standard format (see link below)? That can change people's advice a lot.
In general there's nothing "wrong" with your strategy. You need to shore it up some and get a more focused strategy, by obtaining more copies of important cards. Also, you need to decide what kind of deck you want to play. You have a little aggro a little control (see descriptions below). Blue and white have the ability to completely control the game and you can decide to win with whatever win condition you want. For tokens and taking advantage of your humans/spirits/etc, I believe that black and white provide more here. Cards like Xathrid necromancer, blood artist, cartel aristocrat combo so well, with cards like champion of the parish and doomed Traveler it's ridiculous.
magic formats
http://www.wizards.com/magic/tcg/resour
sanctioned
As far as basic deckbuilding strategy goes.
Archetypes – There are more specific strategies for building decks associate with one of the 3 main archetypes.
Aggro – typically 26-30 creatures, a hand full of removal or burn spells and just enough lands to make sure you can cast your most expensive spells, usually a 4 or 5 cost creature will be the most expensive you’ll play in these decks. These decks build on a pyramid of creatures with 1 drops making up the base, then 2s, 3s, and the top of the mana curve being 4 and maybe… maybe a 5 cost creature or 2. Typical load outs will be as follows.
a. 1 drops – 8-12
b. 2 drops – 8-10
c. 3 drops – 6 - 8
d. 4,5 drops – 4 - 6
e. Lands – 20-22
f. Spells – 6 – 8
Typically no spells with X in the cost you won’t have enough to cast them to any great effect.
Midrange – most mid-range decks run between 12 and 20 creatures with some typically being mana ramping creatures. The creatures that are played usually provide “value” they do more than one thing or are ability packed, provide some kind of combo or provide a measure of control in addition to being threatening on the battlefield. These decks will usually have lots of removal or stall, 12-15 spells, removal or life gain cards with x in the cost, and spells that help them draw or get them card advantage.
Control decks – the only reason you’re allowed to play cards against a control deck is because they let you. That’s the goal. They pack cards that wipe the board and let them search their decks for the cards they need to defeat you. The main goal here is to have the card they need when they need it to stop you from doing what you need to do to win. These are high level decks and require a lot of experience and thought to play.
Mana Base – As a rule of thumb you want a 1/3rd or more of your deck to be mana at a minimum. See some basic guidelines below. Notes these are lands not count other mana sources.
20-22 - Low cost aggro decks, usually topping out at a 4 cost card.
23-25 – typical midrange setup with ramp, fetch, or mana dorks. This will support larger cost creatures and spells and fuel cards with X casting costs.
25-26 – Some control decks will run this amount of mana to make sure they can consistently play their spells without mana fetching or mana ramp.
Less or More – running less lands or more lands than what’s listed here isn’t recommended unless you have a fine tuned and perfected strategy for what you’re trying to do
Resources to expand your knowledge .
gatherer.wizards.com/
• Rules on specific cards and just a general good tool for searching through all the different cards magic has to offer.
www.reddit.com/r/spikes/
www.reddit.com/r/magicTCG/
www.reddit.com/r/magicdeckbuilding
• Spikes provides discussion on the competitive environment in magic
• Deckbuilding is pretty obvious, just another resource for people looking for help building decks.
• Magictcg is just a general discussion forum about all kinds of magic topics.
wiki.mtgsalvation.com/
• Rules database and general knowledge about the game.
www.draftmagic.com/
• Videos and articles about drafting and limited formats.
www.starcitygames.com/
www.tcgplayer.com/
www.channelfireball.com/
• Online stores for magic as well as some of the best written articles concerning magic topics.