I ll try to explain, how I ll find the strumming pattern for a song. If the songs has lots of guitar in it, closely hear the strumming alone and try to play it. You wont get it in first time unless you master in it. But keep trying.
Next key factor is drum beat following in the song. Try to understand the drum beats and try to match the same. You can mute the strings with your left hand and play the drum beats with up and down strokes.
Next one may look funny, but trust me it also helped me to find strumming for some songs. Playing the beats of a song with our mouth(Like TR - tan da na ka, tan da na ka) and play the same.
Strummimg pattern may differ from person to person. You can follow your own pattern. If you can able to match the beats, you can add some fillers(extra up\down strikes) to make it sounds more beautiful.
If any of the things dosent work out, I ll ask help from the seniors in this forum.
Last but not least, Keep playing daily. Dont give up. Choose songs with open basic chords and simple strumming pattern. Once you can able to play it freely, you ll gain lots of confidence.
Hope it ll help you.
"I may be a bad SINGER, but not my GUITAR"