Consider which condiments (or anything else in your fridge/freezer) that you don't need carefully. Toss those you know you rarely/never use. Then consider which really need to stay in your fridge. If you have more cupboard or drawer space than fridge space, perhaps you can keep them there instead (many sauces don't need to be refrigerated, even though it says to sometimes on the bottle... try Googling it).
Plan your meals. That way you won't have to get a bottle of something you only use once. Planning ahead will allow you to either avoid those recipes or give you time to find appropriate substitutions.
One day a week, go through your fridge and use up leftovers and toss mystery packages that have spoiled.
Keep a backwards grocery list on your fridge door, where you write down what you DO have and when they expire. This will remind you to use things before it's too late (stuff in the back or bottom tend to be forgotten), and will keep your electricity bill down a bit since you won't be standing with the door open trying to decide what you want. Also, having this list will keep you from buying duplicates (and show you at a glance what's been crossed off so you need to pick up).
Repackage. Some bottles and containers are really bulky. Buy a bunch of bottles/containers that will streamline things, label them, and fill. Perfect examples are ketchup and mustard. They usually are pretty fat, but those "picnic bottles" are pretty slim and you could keep them in that. Meat can be put in Ziploc bags. All sandwich ingredients like cheese, deli meats, pickles, etc. can be put in a shoe box (or a store-bought container) to corral them. This keeps them all together for convenience, but also keeps them from wasting space (since they're all small, putting each on a flat surface creates unusable dead space above them).
Some cupboard storage units might be useful too, depending on your fridge.
Think of the fridge like a closet when organizing, and you'll have it in great shape in no time.