Make a list of what you want in your next house and compare properties to that list. Be prepared to make sacrafices because there is a slim chance you'll find a home that matches your entire "wish list".
Look at the comparative market analysis and decide with your Realtor the best offer to make. (Remember if you saw a flaw with the property don't be afraid to ask the seller to take care of it. Ex: If the carpet is dirty and outdated, ask the seller to replace it or give you an allowance to do it after closing.)
Write the purchase agreement including all the terms of an acceptable sale for you.