The US Open champion, who has been knocked out in the first round in the last two years, faces Evgeny Donskoy in round two, having received a first-round bye.
The 25-year-old told BBC Radio 5 live: "I haven't played particularly well here the last couple of years. I've struggled so I wanted to make sure I prepared as best I could for these two events in Indian Wells and Miami.
"After Australia I came to Miami to train for three weeks, so physically I'm in good shape. I'm just lacking in match practice and I just hope I can get a few wins here to get my rhythm back.
"I practised a lot and played a lot of practice sets. Obviously that helps but nothing is the same as playing the matches in front of the cameras and big crowds. It's tough to replicate that but you just have to trust the training that you've done and hope that it has been good enough."
Murray has not played a competitive match since losing the Australian Open final to Novak Djokovic in January.