close your eyes, put on your headphones and listen closely. try to identify the different strumming pattern in each chord interval of the song and try following to the beat while strumming (tap your foot, strike your palm or pick against the pickguard whatever...) not that i dont wanna tell you how to do it, its kinda complicated explaining this on the internet.
i have been an acoustic guitarist and trust me, i have been focusing mostly on my strumming technique since i picked up the instrument and have been self taught to the standard where i can quickly pick up the rhythm of the song. what i have mentioned above was one of the methods i used to train myself. its basically practice, and i mean lots of it.
well, for wonderwall....lets just say the strumming pattern is a series of ups and downs in between....thats all i can say
hope this helped
cheers :wink: