Ah, I didn't know some Quakers do more active worship! I have to say, their worship style is not for me, which is why I could never be a Quaker! But that's not to say there's anything wrong with it - it's just I'm used to and prefer something quite different!
I think most Catholic and Church of England churches have service cards which tell you what to say and when to sit/stand/kneel/bow, etc. So you would not have to worry about not knowing what to do. In any case, if there ISN'T a service card for whatever reason, just sit at the back and follow what other people do in terms of sitting/standing/kneeling/bowing. If you choose to keep going, you'll eventually learn the words, no problem!
I'm Roman Catholic but I opted to attend services at my university college's chapel, which is Church of England. I literally had no idea what to do at any point in the service, so for weeks I was just following someone else and what they were doing. When it came to saying stuff, I would just bow my head respectfully. Eventually I got used to the format and then they brought in service booklets detailing what to say and do at each bit, which was very handy