Metal-to-metal contact in your automobile is a no-no. That's why oil and grease are used in many places: The thin film of lubrication they provide keeps the parts from wearing one another out.
Neglecting to lubricate your car's vital parts at the proper intervals, or letting the lubricants get dirty or depleted can lead to calamity.
What can you do to make sure your car is properly lubricated?
The best thing to do is buy a shop manual for your car. It will have a complete section on lubrication, showing what parts need lubricating, with what and how often.
Write down each item that must be lubricated, with the date and mileage at last lubrication and, in parentheses, the recommended lubrication interval. When the mileage or timespan has passed, relubricate and update the entry.
Take steering linkage. Let's say your shop manual says it should be lubricated every 7,500 miles or every 12 months, whichever comes first, and you drive 7,500 miles in 10 months. So the steering linkage gets lubed, and you write down the date and the mileage; at 15,000 miles you would lube the linkage again. On the other hand, if you drove the car only 6,000 miles during the next 12 months, you would relube it after 12 months, again writing down the date and mileage.
Steering linkage, by the way, is connected with ball-and-socket joints, commonly referred to as ball joints. Each ball joint has a grease fitting, and a rubber seal around the joint. The proper way to grease a ball joint is to apply grease through the fitting until the seal begins to balloon, or until grease flows from the base of the seal. Wipe off any excess grease that's left on the outside of the joint. (Some cars have ball joints without grease fittings, or with plugs where the grease fittings would ordinarily go. If yours is one of these, your shop manual will tell you what you need to know on lubrication.)
The nice thing about a shop manual is that it not only tells you when to lubricate, but shows you where to do it.
In general, the items on your car that require lubrication and fluid- level checks are these: steering linkage, engine oil and coolant (check these levels every time you fill up with gas), steering gear (in cars without power steering), power steering reservoir (in cars with power steering), brake master cylinder (brake fluid level should be within 1/4 inch of the top of the reservoir), manual or automatic transmission, battery (check once a month, and for longer battery life use distilled water, not tap water), front wheel bearings and differential (rear end).
A shop manual can be bought through a dealer for your make of car. It's a worthwhile addition to your library, whether you work on your car or have a pro do it.