What's the best way to clean a sensor on a DSLR?

The very best way?

Give it to a camera store to clean, as long as they will replace the high pass filter should they damage it.

Other than that, using a rocket blower to blow the dust off the sensor is the safest way, but BE SURE YOUR BATTERIES ARE FULLY CHARGED WHEN YOU LOCK THE MIRROR UP! You don't want to damage the mirror if the batteries drain and the mirror comes flying back down, and it may slam the rocket blower against the high pass sensor doing untold damage to it, and even breaking it and causing damage to the sensor itself.

If you do use a rocket blower, make sure the rocket blower is clean first of all! No use blowing dusty air into a sensor!

Also make sure you are in an extremely clean environment.

If you have to touch the sensor make sure you are very careful - get an expensive professional sensor cleaning kit and follow their directions very carefully. The high pass filter is quite easy to damage, and once damaged is very expensive to replace!

And again, ensure that your kit is clean, and your environment is clean.

The best way to clean a sensor is not to clean it at all. Use pressurized air to clean it- but I recommend against touching it with anything at all- leave it to the professionals to do that.