Strum Strum Strum

I am having a very hard timestrumming, would anyone like to post somestrumming patterns or how I am to tell how to strum on any music I am trying to learn?

I have watched the videos Strumelia has made but when I start trying to play a song, I can't seem to do the right strum, so I end up - when I am with a group - just doing an out strum. In class today, I was fussed at for not keeping the count correctly but was not shown how to do it. Maybe it's the tabs - when they have the spaces for extra strums - maybe I am not putting in the right ones. Maybe I should be doing a 'sing sister' instead of 'sing sister sister'. Any ideas you would like to offer to help?

Thank you in advance.