The best thing to do is basically to simulate the entire game for each player on the server side and verify every action the player does but this involves a lot more code and is also server intensive for many games.
There also things like signing each request and such but ultimately, the client can't be trusted and will always be able to cheat in some way (like automating clicks and actions via GUI scripting).
There also things like signing each request and such but ultimately, the client can't be trusted and will always be able to cheat in some way (like automating clicks and actions via GUI scripting).