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The way I proceed is the following:
1- set up the camera during twilight (before it is dark)
2- point you camera the way you like making sure your camera is perfectly horizontal
3- do the focus (can use auto-focus since it's still bright)
4- put the camera in mode BULB
5- turn OFF the auto-focus and do not touch anymore the lens focus.
6- set the camera sensitivity (up to 6400ISO with my 5DIII)
7- set up the intervalometer
8- come back when it's dark
9- start the sequence
10- wait for long

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11- transfer all frames to a computer
12- use dedicated software to build the startrail. I used softwares like StartStaX, Startrails, etc... depending on whether you are on windows, mac or linux.
(13- submit it to APOD: https://apod.nasa.gov/apod/ap090314.html)

that's it.

So basically, it's 5-10 minutes preparation. Several hours to wait, 5-10 minutes to transfert all the frames to a computer, 5 minutes to process them. ⌚

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Be extremely careful to a few things that happened to me (do not laught at me):
- check that the lens cap is OUT ?
- check that the auto-focus is disable (otherwise your camera will spend time failing doing focus)
- do not leave your polarisation / density filter on ?
- check that your memory card is not protected in writing ?
- check that your batteries are full
- ....

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Now, I will give you some advices on how to make GREAT or WOW star trails. Everything is about ... the foreground. You can see star trailing everywhere on earth (although limited by light pollution). So what will make the difference is your foreground !
As astronomer, I have the opportunity to make star trail from amazing observatories, such as the European Southern Observatory, in Chile. This is from the La Silla observatory.