It's hard to say what factors will win an appeal, as the panel are balancing the issues faced by the school in admitting more pupils against the needs of the individual child to have a place at that school. If the school's case is weak, the parents are more likely to win by showing that this school would be a better 'fit' for the child.
However, in my experience, many schools are already under a lot of pressure (have already taken bulge classes, increasing SEN issues, financial issues), so only the children with unique circumstances will win.
This might be, for example, children who've been badly bullied at primary want to avoid the bullies, young carers who want to be at school near to home, a child with severe asthma who can't walk far. Really exceptional cases. Often backed up with letters of support from professionals.
That's not to say it's not worth putting in an appeal on grounds of wanting particular things in the curriculum / extra curricular activities, but just be realistic that these may not be sufficient to win an appeal.