Certain breeds need more entertaining than others. Compare a Border Collie to the Boston Terrier for example and you can quickly make comaprisons. Walkies dont have to be as long and extra raining in the week isnt required unless you fancy it.
There are two books i would highly recommend:
Brain Games for Dogs by Claire Arrowsmith
101 Dog Tricks by Kyra Sundance and Chalcy
Both are very well written and provide step-by-step instructions on teaching your pet new tricks.
If you buy a Interactive Toy or make them at home it will provide hours of fun. All are cheap and easy to make.