First off, Harlequin gave a lot of really good tips. I agree with basically all of them, it's going to be tough to add to that list!
1) About how many mana sources do you find yourself running on average?
2) How much of a role does the general play for you in deck construction?
3) What are some of your favorite "staple" EDH cards?
4) How do you go about deck construction in general?
1. Usually 33-35 lands and 5-12 other mana sources (green "ramp" spells, artifact mana). It's proibably not enough though, I get screwed a lot, I just can't bring myself to cut some of my favorites! Also, if your general is mono-colored or cheap (Gaddock Teeg), you can probably use fewer. I have a Kuon, Ogre Ascendant deck with basically just swamps for mana.
2. I like to take a mid-range approach, where the deck works fine without the general, but th general has a strong effect, not just being used for colors. For example, Sharuum the Hegemon: the deck has plenty of internal Esper-synergy, but Sharuum's zombify effect synergizes even more. This is my favorite approach.
My Kresh deck is slightly more built around the general. Many cards (sweepers) are suboptimal without him on board, and a few like Whispersilk Cloak and Shizo, Death's Storehouse are almost exclusively for use with Kresh.
My Kuon deck is built 100% around the general. I always plan to have him in play and flipped, so I make the deck essentially creatureless (There's a Snake Basket and some things like manlands).
I don't really ever pick a general just for the color scheme, although I am considering a Horde of Notions deck primarily so I can play Maelstrom Nexus.
3. The green ramp package (see my Kresh list) seems like it should go in almost every green EDH deck. Beyond that, Hinder is one of the best counters. The #2 card I think should/could be in every deck though is Solemn Simulacrum (#1 is Sol Ring of course). I'd probably even put SS in Kuon!
4. Deck construction for me begins with thinking of something I want to do: for example, I want to play with Maelstrom Nexus, so I had to pick a 5-color general. Or another project I'm tinkering with: I want to play CIP creatures, sacrifice them to some profitable effect, and recur them with Oversold Cemetery or Phyrexian Reclamation. So I picked Thraximundar as general, and pulled out a list of about 200 potential cards to use, and am working on paring it all down into a usable decklist.