Kotaku has an article at http://kotaku.com/how-to-beat-400-games-in-4-5-years-1607296068 on one person's advice on working through a backlog and beating 400 games in 4.5 years. The tips are relevant to getting any large projects done, and not specific to just gaming.
As with most tips on getting things done, it involves having active support from a community ("find a friendly online community interested in beating games together"), plan ahead ("determine for yourself what counts as 'beating' a game"), document progress ("get in the habit of tracking your games"), use tools to help tracking as needed ("learn to use HowLongToBeat.com and plan your time carefully"), creating a system that allows you to work toward your goals at all times ("embrace the accessibility of digital, mobile and portable games", allow some free times to brainstorm ("allow yourself to occasionally play games without the intent of finishing them"), re-evaluate and allow yourself permission to give up on projects that are no longer relevant ("move on"), and finally, have small accomplishable goals ("think about short-term goals")