Determine the type of washer and dryer best suits your needs. Washer and dryers can be stacked, side by side and unitized. Stacked means that you can stack the washer and dryer on each other to conserve space. Unitized is an all in one washer and dryer in one appliance.
Determine the capacity that you need. Most people opt to purchase a large capacity washer and dryer regardless of if they have a large family or not. You will save electricity by being able to washer all of your clothes in one single load rather than running two loads.
Look for a washer and dryer that have the energy star sticker. Energy star washer and dryers save a lot of energy compared to their counterparts. These might cost a little more but they will pay for themselves in the first year on average.
Read reviews. Their are reviews available online and in magazines. Washer and dryers are constantly reviewed by companies and given a rating. Check to see if the washer and dryer you are interested in purchasing received a good rating before making your purchase.