The age old advice holds, shoot more.
Different situations and conditions means we can't give generic mantra on what settings to use. Post your pictures for criticism (with their exif data) if you are not sure how it can be improved (technically).
If you could tell or show us your problems in your photos, we could help you.
So, what is the problem with your 18-55mm lens?
I think its a common approach of most new DSLR owner to have one lens "to cover all ranges", maybe they are used to the xx times zoom of the compacts. If you really want a long reach, keep the kit lens, get the 55-250 IS as an additional lens.
There is a thread on the Canon forum on the 18-200mm, search the internet for more reviews. Finally, rent the lens if you really want to convince yourself.
Go out and shoot, come back with photos, find out what's wrong. If you don't know, that's what we're here for. How are we to advise you on the camera and lens? I mean we all could advise you on how to hold your lens, turn the zoom ring and so forth, but ultimately YOU are the photographer.
And I hope to not be rude, but I personally feel that although your dad has all the rights to not like your camera, he's not the photographer-- you are. So, do you hate your kit lens?
EDIT: Don't put up pics when you go out to shoot. Chances are you already have a few photos that you and or your dad doesn't like. Post those up for us to see.
The price for the 55-250 might not be updated, but its thereabouts. Certainly beats spending $1k+ for the 18-200mm if you ask me.