Car not starting sometimes

If as you say the vehicle clicks when it doesn't start it tends to indicate an issue with either the battery, connections, or the starter motor itself. Make sure the battery is charged up and have a garage do a drop test on it, this will help determine the batteries condition. Also check ALL cable connections between battery and starter motor, including chassis grounds for bad connections. It's also possible the starter is on its way out, so removing it and testing it would be a good idea if the battery and cable connections etc are all found to be good. A faulty ignition switch is also a possibility, but not nearly as common as the things I've listed to check here.

There's such a wide array of options to check for when you have a no start or a hard start, a car is run from a computer that sends signals to wires and components in your engine that have a if / or statement that is redirected back to the main PCM, if it detects the error, no start or hard starts occur...

Just a few options to check

 Ignition key cylinder
 Battery terminals
 Starter solenoid 
 Coolant temp sensor 
 Crankshaft position sensor
 Fuel pump
 MAF sensor
 PCV valve
 Cold Cranking Amps
 MAP sensor
 Fuel regulator
 Coil pack
 Spark plugs
 Spark plug wires
 Fuses

Just to name a few of the functions that get called to the main function while igniting, if they aren't functioning. Then blaa

And then your alternator will keep everything chugging along

Although a click click at random times sounds like a low cold cranking amps of the battery, an ignition cylinder issue or a starter solenoid going back

The fact that you're jamming the key in raises concern, there's spring loaded push pins in there that you don't want broken

I would try by-passing the ignition switch, with a set of wires with alligator clips on one end and a start button on the other Hook one on the small post on the solenoid and the other to the positive side of the battery and push the button if it starts then do it a few times and if it doesn't have the problem as with the key switch then you know it inside the car and not in the engine compartment. They have a remote starter switch and you can probably borrow one from Auto Zone. You can also use just a wire to jump connection from the solinoid to the battery but you need to be careful.