Your white Apple Keyboard (old generation) is very dirty ? The keys are hard
You can disassemble it very easily, and vacuum it in about 20 minutes.

After this dust, your keyboard become white again and the keystrock easier.

This Instructables is also possible with other keyboards.

Step 1: Disassembling of the Keys

Use a coffee spoon than a lever to remove the keys.

Step 2: Sort the Keys

You can sort the keys in a plane surface. It will be easier when you must reassemble the keys.

Step 3: Vacuum the Keyboard

Give the keyboard a quick going-over with the vacuum cleaner.
You can also sweep the keyboard with a wipe (I used a wet baby wipe) in the denuded keyboard.

Step 4: Reassembling

Now, you can reassemble the keyboard.
Take a key and replace it : put it in the right place and press it highly.
In the big keys, there are an small iron wire : be careful to replace it correctly.