Have the established churches somewhat more proactive in fixing the glaring faults in their systems. (Not talking about the religion in itself, the organisations build around it).
If the church is less rocked by skandals (golden bathtub, child abuse), arch conservatism and more willing to accord to a modern worldview... then less peple would look for alternatives and keep with them at least nominally. Sadly in many regards the churches are very... göacial in terms of modernising and stick to institutions established in the dark ages.
If you tell people that they don't belong, they will go elsewhere.
The church has alot of answers to peoples problems, but not all the answers fit a modern world view anymore. LGBT, immigration, feminism, egalitarism are here to stay, and the church would do well to accept that and chance their stance on these things. (looking especially, but not exclusively at the catholic church there).