I am BRAND NEW, and everyone on this site is smarter than me, but this is basically what I have done:
I watched a few youtube videos about cleaning and sanitizing corny kegs. And I have done a lot of reading on this site.
I built a line cleaner following these instructions:
https://www.homebrewtalk.com/f254/diy-beer-line-cleaner-226497/
I use starsan. I also have a wallpaper tray like this (
http://www.homedepot.com/s/wallpaper%20tray?NCNI-5)
that I use to soak long items in to sanitize which, if I remember correctly, was a tip from searching this site.
I dipped the parts, (connectors, lines, etc.), into sanitizer as I assembled. Maybe a little overboard, but that's me. Then used my line cleaner to wash, flush, and sanitize lines.
I use oxyclean free to soak and clean the keg and little pieces. I bought a used keg and changed the o-rings. I have o-ring lube on hand when assembled. Then a real good rinse of all parts and put them in starsan. When assembling the little parts of the keg I took the pieces out of the sanitizer and assembled.
Filled the keg about 1/2 full with sanitizer, shook, turned upside down, shook, let it set in upright and upside down for 10-15 min. each, drained and then racked in beer with sanitized tubing. Sanitize the the posts and make the connections. Wait for the CO2 to get dissolved, about a week, drink, smile!
Don't introduce oxygen when you transfer, the transfer line should go to the bottom of the keg to prevent splashing and let it fill from there. As long as the transfer line is sanitized, inside and out, no problem.
Starsan is a little harsh on my hands so I use gloves, nitrile or latex.
Other, more experienced brewers, will chime in and hopefully I haven't given any bad info.
Good luck and enjoy!