I am afraid that there is no real easy way or short cut here, its just down to practice. These things take time to master, adding dynamics to a strumming pattern and playing more intricate rhythms are things that come with time. Just keep at it, play every day, challenge yourself to come up with fresh rhythms and you will continue to improve.
You have to challenge yourself in order to move forward or you will end up stagnating. Time, time time. Thats all you need.
Good Luck!