1. Twitter - share your own ideas, learn from others and engage in educational debate. The debate and discussion will help to develop your own educational philosophy and the values that you believe in. In interviews, you will be questioned about this so it's good to develop one and share it so that you fully believe it too.
As much as you are able to move around. Within your school move around to as many different year groups as you can. Many teachers believe in staying in the same year to gain experience of that year group. However, they are just repeating one year of experience. This year, is the first I have stayed in the same year group. Going into Foundation stage was a brilliant experience that allowed me to see the starting point of children and also unpick the key issues within the school. Moving from Foundation to Year 6 was again another excellent personal learning experience. Understanding the process of external tests is also essential for the move into SLT. Finally, and this is dependent on your situation, try to move to a variety of schools. Working in different sizes of school and socio-economic areas really broadens your craft as well as your outlook on teaching. Teaching a hungry child is much more of a challenge than teaching a child who has lovingly been given their breakfast. Increasingly, schools have been looking for candidates who have worked under different LEAs so moving further afield could be advantageous.
3. Apply, Apply, Apply
Apply for jobs. Be honest with your headteacher, a good head will always support you and often give you an insight into the type of school you are applying to. Writing your covering letter and selling yourself are skills that can be honed. Most interviews will gave a teaching, presentation and interview element. Depending on the school, you may also gave a data task or a letter writing task. Usually this involves creating an action plan and explaining how you would implement it. Practising these skills under pressure at interview will prepare you for the next step.
4. Personal CPD
Go and speak at Teach Meets, conferences and staff meetings. This helped develop my confidence enormously. Not only in speaking to large audiences but also the confidence to believe that what I was doing in my classroom was worth sharing. And if you don't have a Teach Meet nearby.... Organise your own. This is a great asset to bring to an interview for SLT, knowing that you can organise a CPD event and how this has developed you as a leader will always create nods in the interview room.
Depending on your circumstances try to volunteer for as many things as possible. During a busy period, offer to cover a playground duty so that you solve a problem for the SLT. The same applies to assemblies, being able to 'stand-in' and making it known you are capable is vital when moving from a classroom to whole school outlook. Become a school governor: having an in-depth knowledge of how a school runs is an enormous advantage. If possible try and join the business committee, as a teacher, you will know about teaching and learning within your school, understanding the impact of staff sickness, building repairs and asbestos really help give you an idea of what is needed to run a school. Lastly, always try and run an after school club throughout the year. This gives you a chance to work with children in other age groups and increase your reputation around the school. The more you give, the more experience you'll gain, which can then be used as examples in the lottery of the interview questioning.
There is obviously a lot more to becoming a senior leader than this, but I really felt that these things have given me the edge in interviews, especially when coming against colleagues with twice as much experience as myself. My final suggestion would be to ensure your safeguarding knowledge is up to date and you have some experience in following policy. Good luck if you are applying!