If you want to make a famous mission follow my steps:
1.In your mission you can put explosions after timeouts to make it more harder to beat!
2.You can make your mission long and difficult by adding more health to enemy actors!
3.You can make it more scary by selecting weather with fog and scary actors,but and with sounds with the v7.02 and hide them after some checkpoints
4.Don't add to player minigun because it make mission more easy!
5.Select a theme like swats vs terrorists,horror,etc
6.For your mission you can make a trailer to grow the mission popularity.For the trailer of the mission you can edit intro and put music,but when selecting music it need to reflect the theme.An example:If you want to make a trailer for a horror mission you need to put scary music or it doesn't get sense!