As a wrong side of 30-something referee who trains twice a week in the season and refs most Saturdays, I tend to slow things up on the training front in May and do little during June, apart from a weekly game of cricket!
Come July, I start with a weekly jog of around three miles, cricket and touch rugby, and then build in a weights session.
In August I concetrate on sprint work and the three-mile run is replaced with a fartlek session, and a weights session.
Build into that a few pre-season friendlies, and it seems to do right by me.
Someone mentioned core strength work and this was introduced to me last summer down the gym. It's proved very invaluable and as such I think helped eliminate any potential niggling injuries.