The skeleton of my decks usually look something like this:
38+ lands (more of you have a high CMC average)
~10 ramp/mana rocks (more of you have a high CMC average)
~10 card draw spells
~7-10 Single target removal spells
~4 board wipes
The rest are all cards that support the theme or strategy of the particular deck. Usually, I also have at least one card that can remove cards from graveyards or entire graveyards. My meta isn't extremely competitive though.
This, think in categories of cards and never skimp on the ramp/draw/answers