1. Switch the side of your mouse-pad
Yes, it is as simple as that.
By switching the side of your mouse-pad you will force yourself to use your non-dominant hand. This, in turn, will stimulate the neural connections between the right and left hemispheres on your brain. Scientific research confirmed that people that use both hands equally have 10% more nerve fibers joining the two sides of the brain.
Ideally you want to perform as many activities as possible with your non-dominant hand, but some of them might become cumbersome. I tried to brush my teeth using my left hand for one week or so, only to find out that the tartar was building up.
Using the mouse with the opposite hand is something that you can easily integrate into your life. During the first couple of days it will feel weird, and you might need to switch back when using programs that require intense "clicking" sessions. After this adaptation phase however, you'll be navigating the computer just as efficiently with both hands.
2. Force yourself to remember things
Sometimes you want to remember the name of a song that is playing or the name of an old acquaintance that passed by . It is right there, on the tip of your tongue, but you can't remember it. What would you normally do in such situation? Probably ask some nearby friend for the name, and upon the revelation you will even shout marveled, "Oh yeah! That is it."
The next time this happens force yourself to remember that name. The brain can be stimulated just like your muscles and the more you exercise it the stronger it will get.
Do not limit yourself to remembering names. Are you calling your mother to get the phone number of your uncle? Forget pen and paper - you can memorize it. Try to look at the keyboard of your phone in order to create a mental picture of what the sequence of numbers looks like.
The worse that can happens is that you will need to call your mom again...
3. Play games that involve some thinking
You don't need to participate in the Mathematical Olympic Games in order to stretch your brain capabilities. Oh no, games and activities as simple as sudoku or crosswords will already have a tangible impact upon your brain performance.
Regularity is very important here, so try to incorporate these games or exercises into your routine. You could bring a crosswords book with you on the daily commute, for instance. Personally I like to play a chess match every day before I start working. It takes around 15 minutes, but it ensures that my brain gets a kick-start every morning.