That is tricky. After all, if you find a purchaser for your existing home, before you have found a new one, you may find yourself living out of a suitcase if convenient closing dates can not be negotiated. On the other hand, if you find your dream home before you unloaded the old one, you may be faced with carrying two mortgages for a time.
So how do you manage?
Do your homework and have a good idea about the neighbourhood and type of home you're looking for. Do an honest evaluation of your family's income, needs and budget. Speak to the right agent and start your new home search as soon as your existing home hits the market.
If you have found a home, before you have sold your existing one, use "sale of your existing home" as a condition on your offer. If you don't sell your house within a fixed period of time, you can choose not to go through with the offer. This however, is a difficult condition for many vendors to agree upon and you may find that you have to forgo your price negotiating power. Purchasing a home before you sell could be a risky strategy if you're counting on the proceeds from the sale.
If you have found a purchaser before you have found your next home, use "purchase of a new home" as a condition when you sign back the agreement. Again, it will only be for a fixed time. Even if you have not found the ideal next house by the time the deal closes, you may still wish to proceed with the offer. As a buyer with a "sold house" you will be in a better position to negotiate price.