At 360voice I worked hard to get to 25% and maintain it, now I'm up to 30% with 23 achievements to go until I hit 31%. I'm trying to not play new game but revisit previously played game and re-renting those backwards compatible. I do have games such as GTA IV which has like one achievement unlocked and we all know that games a bitch to run on PC! Even GTA V ran on my computer yet GTA IV wouldn't....
I have other games such as Halo with it's bazillion achievements (I have 6% unlocked). There are also some old Xbox 360 games and hopefully they come on the Xbox One soon. I know there was rumours about Left 4 Dead or Left 4 Dead 2 and I could get some cheevos from them.
At the minute I'm working through AC: Unity with the premise of possible knocking out 4 achievements at least to finish campaign and a few mop-up ones.
Getting to 50% is quite a challenge. It may not happen but I'll change myself to the end of the year!
I was in the same boat trying to get to 90%. Once I hit 90% here (Sitting at 88% on TA) I lifted the the new games rule for myself. You might also want to try to complete 2 games before you start a new one.
It won't be long before Xbox and it's developers will put a block on the last mission until you get every achievement just so 100% is 100%. Once I complete the game I don't really want to play it again. I completed Lego Marvel Superheroes but the 100% cheevos is only one I don't have.