Here is my tips.
Sit in a room alone (without your guitar). Turn the music on (of your choice), turn off the lights. Try to follow the rhythm of the music and tap along (with your foot, your palm on your lap or tap your chair) with the music. Feel the music & the rhythm. Do this always... then get back to your guitar... the next thing you know you will strum the music naturally, by just listening to the music before you play..
Sorry if my English is hard to understand. That's what I did after frustation learning from the books and I am improving a lot now.