Make sure the car is in neutral and handbrake is on before starting. It's not strictly necessary but you should make this a habit for safety.
Buckle up. Make yourself aware of your surroundings.
Insert and turn key / press button. Newer cars require clutch and/or brake to be pressed to start, check the car manual if unsure.
Key shouldn't need to be turned for long - if its kept turned when the engine starts you'll hear a horrible grinding noise. Avoid this.
The car should now be started. Take your foot off clutch/brake, nothing will happen (as long as you ate in neutral with handbrake on).
To start moving, press the clutch, put the gear stick in 1st, start smoothly lifting your foot off the clutch. You're looking for the bite point of the clutch - when you start to feel the car want to move. This takes practice and you will stall the car many times before its natural. Once you've found the bite point, its time to release the hand brake*, and start gently pressing the accelerator as you lift your foot the rest of the way off the clutch.
It takes a while for this to be smooth.
*you could release the hand brake before this and use the brake pedal instead.
When you want to change gears, take your foot off the accelerator, press the clutch, move the gear stick to the right gear, release the clutch smoothly, press the accelerator
How do you keep getting locked out? Would it not be easier to remember your keys when you go outside?