Getting Started With systemd on Debian Jessie
medium.com
medium.com
Don't start by editing the file permanently. If the worst happens (typo, whatever) you're either not going to boot or have a somewhat rough time of it. So the first thing you do is boot, in grub hit "e" to edit the boot, find the kernel line and the "quiet" parameter (most likely) then edit/add the init line as seen in the article. Then boot. Did it work? Cool, think about making it permanent. If it crash down in flames? Well, no problem, that edit wasn't permanent, just reboot and its all good. When/if you make it permanent, if you make a typo, you can edit to boot and fix it using the same "hit E to edit" technique you just used to test, so no fear.
I made the change permanent on Jan 6th on my work desktop and its been pretty boring indeed since then. Just works. I'm not personally very happy with the design, but so far it hasn't bit me.
Its possible to put some significant effort in and permanently remove sysvinit but its easier just to install both in parallel and simply boot into systemd. As far as I could find as of a month ago there was no problem having both sysvinit and systemd installed simultaneously and select at boot time. Someone with more time on hands/motivation could make an entirely new grub stanza to simply select from the grub menu if you want sysvinit or systemd.
Its a good article other than that minor "test before making permanent" thing.