Utilize coincidences to come up with ideas
Sometimes, when you're walking through the city, you see something that inspires you and gives you a good idea.
Such coincidences may also be enforced. You could open a random page of an encyclopedia or a dictionary, and pick a random word (a noun) on that page.
For example: You're developing a logo for an online bookseller. The random noun you picked is "effort".
Search for associations with the word "effort". Write them down into a column, one below the other. Draw a second column next to it and think about logo ideas that go with the lefthand association and the online bookseller.
This is another good method to come up with new ideas. Even if it sounds a little strange, this method is frequently used.