Look in any decorating magazine and there will be a room with baggy, white or natural slipcovers. It's the perfect canvas for all sorts of eclectic decor. I don't do slipcovers. I never learned how because I've always had neutral upholstery fabrics on my furniture. However, seasonal slipcover changes seem like the ultimate luxury. Light and fresh in the Spring and nubby, warm and cozy in the Fall, ah yes.
If you need to cover up some disgusting stains and you have a sewing machine, you can pick up cotton duck very inexpensively. Here's a complete chair slipcover tutorial from Pink and Polka Dot from a while back. It still works.
You'll need more yardage for slipcovers than if you were reupholstering, so here's a chart to determine slipcover yardage.