Goodreads Authors/Readers discussion

I was just hearing about how its never too late to relaunch one of your books - meaning that a book launch isn't a one-time, initial thing, but something you can do whenever you want - or even should do every six to twelve months or so. I'd never thought of that before. I'm thinking of doing this for a Kindle title that's about a year old and was trying to come up with a strategy. My last "launch" consisted of just letting people know on social media, but that was about it. I'd prefer to not spend much money ... but this time around understand it might be necessary to at least spend some. For those of you who have successful book launches (or re-launches), what did you find helpful?