- Balance the land - around 40 in an 100 card EDH deck and about 20 in a regular 60 card deck.
- Check mana curve - you want a decent spread of 1 to 4 mana spells with select 5 and up spells.
- Non-creature to creature ratio - this depends on your deck, but you always need some creatures.
When I want to make a new deck I sometimes like to use the site DeckStats. You can create your decks by searching the database and dragging and dropping cards into your deck. Afterwards, you can see a nice little graph and pie chart showing things like Mana Curve, Card distribution, Mana distribution, and Mana Source distribution. Then, you can save your deck (just make sure to make a profile on the website).
For example, here's what my Tymaret deck looks like on DeckStats.
I can easily see that the majority of my spells are quite cheap with 3 mana spells being my most abundant. From this I can hope (getting mana-boned happens to the best of us) that I shouldn't have trouble getting most of my spells out.
With this pie chart I can easily tell that I have more black cards than red cards (shown on the left). This will inform my decision on how many swamps and mountains to put in the deck (shown on the right). Taking the information from the previous pie chart I made sure that my Swamps and Mountains were balanced to accommodate my deck being more black. I've made sure to add a few more swamps (20) than mountains (16) in this case.
There we go! There are others things to consider when making a deck of course. The specific abilities and effects the cards do are also incredibly important! However, I like to use DeckStats because it keeps me organized and lets me quickly see at a glance the other information to keep in mind when making a deck. Happy deck building!