The first thing is to check that the engine is intact and has an oil filter attached, cars often get left due to a break down or due to unfinished repair work. You then check that sufficient oil is present, don't worry at this stage if it's as black as Hades. Connect a fresh fuel supply to the carburettor or to the electric fuel pump if the car is fuel injected. You'll obviously need a fresh battery, and you'll need to remove the spark plugs and squirt a few drops of fresh oil into each cylinder. You then turn the engine crank pulley gently a few times by hand to free it up and ensure nothing is binding. After you're satisfied that the engine is turning over freely, use the starter but leave the plugs out, that gets the oil circulating through the engine. If all sounds good, refit either new plugs or the originals after checking they're still serviceable and correctly gapped, but do not fit the plug wires/coil packs to them. Operate the starter again a little and check for odd noises. Finally, reconnect the plug wires/coil packs and operate the starter again. When it starts expect loads of smoke due to the oil you squirted into the cylinders.
Doing that often means I've managed to start engines which haven't been run in over thirty years, my oldest was a 1930s Lagonda which hadn't been run for fifty-eight years.
If the engine has a functioning cooling system then warm up the engine and check for leaks of any kind. If you're moderately lucky all will go well and you'll then find that it's worth investing in an oil and filter change, and you can check the condition of the generator belt.
After that you'll normally find that the clutch (if manual) has seized and will need freeing off, and likewise for the brakes. The exhaust/muffler will usually be severely rusted and in need of replacement, and the tyres will definitely need replacement as they'll have perished even if they look externally perfect.
Very hard. It pays to squirt oil into the cylinders to free off the piston rings. The fuel will have turned to rubber so cleaning that out will be a challenge. You will also be lucky if the brakes haven't seized and, if manual, the clutch may have bonded to the flywheel with rust. Good luck, you'll need it.
some will fire right up after you get new gas, plugs, points, rotor etc, but, before starting or turning the engine over I would remove all the spark plugs and put some penetrating oil in each cylinder then let it set for a day or two then pour a small amount of oil 10w40 into each cylinder and let it set for a day, then try to fire it, reason being is if the rings are rusted or stuck to the cylinder walls this will help in preventing them from breaking!
Don't try to start it. If oil and fuel was not drained properly and if rustproofing was not done, you will have one glomed up mess inside the engine.
