#1. Know what your primary stat (your "attack stat") is. Make sure that stat is at least 18, after racial modifiers. If you have a choice of primary stats, pick one and ignore the other.
#2. Know what your secondary stat is. Make sure that stat is at least 14, after racial modifiers. If you have a choice of secondary stats, pick one, but a little love for the other is not a bad idea.
#3. Pick skills and powers that play to your high stats. Look for powers that key off your secondary stat; look for skills that key off your primary and secondary stats.
#4. Pay close attention to your class features. You can figure out powers and feats and stuff as you go, but understanding how your class features work is central to playing your character.
#5. When taking feats, look for feats that give simple all-the-time bonuses. The advantage to such feats is twofold. First, they're usually the most powerful choices; and second, you don't have to think about them in play. A feat whose benefit you always forget to use is a feat you might as well not have.
#6. Plan on taking an Expertise feat early. It doesn't have to be your absolute first pick, but you really want Expertise in your chosen weapon/implement before you hit Paragon.
(These are not, of course, ironclad rules. There are cases where an advanced optimizer might choose to break any of them, except maybe #4 and #6. But this is one of those deals where you should understand the rule and the reasoning behind it before you decide to break it. If you're building a tactical warlord and decide to leave your Strength at 16 so you can get that sweet, sweet 18 Intelligence, that's cool, but you need to understand the consequences of that - for instance, Commander's Strike goes from "very strong pick" to "vital necessity.")