The others are on the right track, however you always want to keep in mind your intended playgroup. What works with some people won't work with others. If you plan on playing at the club though, a fun, casual outlook is generally all you need.
However, there are a few "staple" cards/concepts that you should probably be aware of which are just really good for handling certain problems. Obviously if you have another way to solve said problems they may not be necessary, but I for one generally won't leave home without certain power pieces:
White:
Some sort of wrath effect (Wrath of God, Hallowed Burial, etc.) - Used for clearing problems like Kozilek, Progenitus, and swarms of tribal dudes.
Path to Exile/Swords to Plowshares - Gets rid of indestructible creatures. Any spot removal that exiles is good. Bottomdecking cards like Condemn and Bant Charm are also very useful.
Blue:
Counterspell/any other hard counter - If you need to just say NO, this is what it's here for. Used in situations where an opponent resolving a spell will win them the game, or kick you out of it.
Green:
Artifact/Enchantment destruction - You'd be surprised how many enchantments and artifacts our group runs, yet how few removal spells we run for it. Obviously other colours can often perform this function too (white's disenchant or any red artifact destruction spell), but green is the most proficient at it, so I put it here.
Black:
Creature spot removal - Whether you're packing Doomblade, Go for the Throat or a Damnation, black's got creature removal. Run something. You'll thank me. Even Shriekmaw or Innocent Blood, whatever works for you. Remember, people often win by attacking. The less creatures they keep, the better for you.
Red:
Red actually doesn't have too many staple cards, but if I had to pick one, I'd go with that artifact destruction I mentioned earlier. Past that, you're more or less free to synergize your red pie with the rest of your deck.
Artifact:
Depending on what colours you're running, this can change. Sol Ring is an auto-in whatever you run, and for multicolor decks cards that mana fix are good bets. Monocolor decks tend to stick to stuff like Gauntlet of Power and similar effects for ramp.
I tried to avoid namedropping expensive cards, and instead tried to stick to staple "themes" (what every deck should be capable of doing). Hopefully this helps.
PS: Bodies with abilities (we also call them "sticks") are very useful when their triggers or activated abilities perform the effects I mentioned. Shriekmaw is a good example of a Terror on a stick. This is especially helpful when the stick also synergizes with your commander or other elements of your deck.
PPS: Make sure every card in your deck either works toward your commander's purpose, or does not interfere with it. The best builds utilize your general, but do not necessarily rely on it to succeed. Hope this helps!