If the interior of your Filofax organiser is cloth or part of it is cloth and it's starting to look a little 'grubby', mainly from paper dust, try this.
Open your organiser and lay it flat. Take a length of sticky tape or packing tape and press the sticky side down on to the cloth and then lift the tape off. Repeat this with a new length of tape until you have done both front and back of the organiser.
The dust will stick to the tape and leave the cloth looking like new again. The tape shouldn't leave any residue behind as it is only on the cloth for a few seconds.
For the leather covers, I use an ordinary household silicon based spray polish. However, before you try this, I would recommend using a small amount on a small area of your organiser to ensure it will not alter the colour of the leather too much. My organisers are mainly dark colours so any colour change is not noticeable.