I would take the paper he has weed on inside outside, that way it already smells of him and he should get the idea that he can go on the paper outside, also with the paper left inside its sending out confused signals and he proberly can't understand why hes not surposed to use that.

There is a spary you can get which you spray where you want the dog to go, I found that helped with mine, also taught him that he could have a wee in the woods (prior to that he saved it all up for the garden when he got home!) as he got used to the smell and assicated it to where he could go.

I think the rule of thumb is that after every meal/drink/nap/playtime you need to go out, and if he has a specific place that he is going indoors then keep our eye out for it, if you can then sit near it then when your dog does his tell - walks in a circle, tail up etc. then you can call "outside" all happy and exicted and run to the door. he will soon learn to go to the door.

I always gave mine a treat when he went outside and gave lots of praise.

It can take a lot or time and patientce so good luck and just stick with it!