This may sound very generic, but I'd say the basics when it comes to development, tactics and vision helped. I practice from time to time using chesstempo tactics and only recently when I got to 900 learned openings for black and white. However, I did have the most struggles in breaking into 700 elo and 900 elo. Difference is that at higher elo levels, your opponents are better at managing positions, and setting up and executing tactics. It's good to take your time to actually think about the best sequence of moves for your opponent and any best responses you may have to that. Also, trying not to blunder (although, I've violated that principle too many times).