Some tips for cleaning vertical blinds are to dust them first, to leave them hanging while you clean them and to place a towel or tarp underneath the work area. Another tip is to perform weekly cleaning to avoid major build-up of dust and dirt over time.
Before using any kind of cleaning product on blinds, use a vacuum or a lambs' wool duster to knock off excess dust. Don't use a rag for this step, as this can just smear the dust into the blinds instead of removing it. Vinyl, aluminum, fabric and wood blinds are usually easier to clean while they are still hanging up. Trying to wash removed blinds in a tub or basin can result in cracks or tears if you are not extremely careful.