MIAMI – Britain’s Andy Murray says there is plenty of room for improvement as he heads into the clay-court season ranked number two in the world.The Scot beat David Ferrer to win in Miami on Sunday, taking him past Roger Federer in the latest ATP rankings.  Murray remains some distance behind world number one Novak Djokovic."It’s good to get there but I obviously want to try and keep improving,” he said. "If I get the chance to go higher that’s what I want to try and do.”There had been lots of talk around Murray’s potential ranking improvement during the Sony Open in Miami, and the 25-year-old admitted he was relieved to get the job done ahead of the busiest stretch of the season."It was nice to get there so I can go into the clay-court season just focused on improving and going forward and not worrying about rankings or seedings or anything like that,” Murray told BBC Radio 5 live.Murray described clay as "my worst surface” but he is a former French Open, Monte Carlo and Rome semi-finalist, and has the opportunity to close the rankings gap on Djokovic this year after failing to make it past the quarter-finals on clay in 2012.However, the impressive return to action of seven-time French Open champion Rafael Nadal after nearly eight months out with a knee injury leaves little doubt over who is the favourite for the major clay titles.A potential benefit of being ranked number two is, given an ideal draw, he could be placed in the opposite half to Djokovic, Federer and Nadal at the French Open in May.