In a very genuine sense, I would put more emphasis on PE as a means of developing teamwork as well as improving fitness; but I'd diversify it - it's not all about football for boys and netball for girls, which is mostly what the secondary schools in my area 'taught'. Other subjects I'd develop would be computing (whilst retaining IT as a separate and distinct subject) and look at making some of what used to be called 'citizenship' subjects in their own right - law, politics, sociology etc can be just as interesting to children as A-Level students, parts of them were to be even without teaching in schools.
I'd start listening to teachers about their experiences and work with them, pupils, universities, and employers to develop policy changes to the curriculum and qualifications. I don't want to go on an anti-Gove rant, but he has more than once put out consultations then ignored the responses in favour of his ideological agenda. That's not the way to do it.
I would try and ease some of the workload on teachers. This might mean having more teachers to cover roughly the same number of classes so that there is more time to mark, write focused feedback, and reduce the out-of-hours workload involved in teaching, or it might mean bringing in teaching support to aid with some of the tasks whilst not taking control, understanding of pupils' performance, and authority away from the teachers themselves.
To encourage improvement in teaching, as opposed to simply standards-meeting as ensured by Ofsted inspections, I'd want to set up a network for best practice, where those who innovate in teaching can share what's worked, what hasn't, and how pupil support can be developed positively rather than simply not-negatively.
I don't think we actually have as bad an education system as is often made out, but what does do damage and prevents progress is the continuous tinkering that goes on with it. There's not enough time for policy ideas to be evaluated medium-term before another initiative is brought it which throws it off kilter. GCSE reforms are a prime example of this, with announcements of reforms in 2010, 2011, 2013, and a timeline of various changes taking place between 2013-16, and even then it's a lot of changes which individually are then made incredibly difficult to measure the impact of.