The best thing you can do to minimise corruption is to make it necessary to bribe so many people for the corrupt to achieve their goals that doing so would be uneconomical. The reason Qatar is hosting the world cup right now is because FIFA has a very small selectorate, and therefore it's only necessary to bribe a relatively small number of people to swing the vote.
Or you could just have strong (and enforced) laws that greatly limit how much power politicians have and then you wouldn't have to keep all these additional layers of corrupt politicians, institutions and government bureaucrats fighting with each other about who gets to be corrupt every 4 years.
How to achieve that is left as an exercise for the reader :)
There is no way to ensure reliable and honest politicians. The best you can do is hope most policymakers are at least somewhat honest, and then institute stringent checks and balances to ensure a corrupt politician can't do too much damage. Which is what most developed democracies do, with varying degrees of success.