Price manipulation needs quite a bit of liquid assets, so you would only do that if your profit from the changed price can exceed the costs of the price manipulation.
Just asking more for your bitcoins when you try to sell them would not really work, market mechanism determine the actual price, not individual bitcoin sellers.
The most promising approach to increasing the bitcoin price would be to offer more goods and services in exchange for bitcoins, making it more attractive for people to own bitcoins and pay with them. This would work best for services that can't be handled well with traditional payment methods, which is why the unfortunate link between silk road or gambling/betting and bitcoins exists. SR certainly caused some of the bitcoin price increase.
With the recent adoption of bitcoin payment options by more mainstream businesses, the price will hopefully increase while the shady image of bitcoin as payment for illegal stuff will be corrected somewhat.

Onkel Paul