Love the Lake District.
Always stay at The Hilthwaite House Hotel in Windermere. Superb hotel with absolutely first class food at a bargain price.
Depends what you are into really. If you fancy walking then just grab a copy of Wainwrights Walks and do a few of them.
If you are more interested in places to visit try:
1. Keswick, lovely little town. You must visit the Old Friars Chocolate Shop. If you are a chocoholic like me you will love it.
2. Bowness on Windermere. Another lovely little place. Some great shops and you can catch a ferry across Windermere. Very scenic.
3. Rheged Centre. This is near Penrith and is built inside a hill. Also has an huge Imax Cinema if you are unlucky to get a rainy day.
4. If you have a reliable car, drive over Hard Knott Pass. Very very tight but beautiful landscape.
5. Grasmere. Another beautfil little village. Famous for the Grasmere Gingerbread shop.
I could probably go on for ages here, there are tons and tons of superb places to visit in the Lake District.