To book a hotel in Paris

If you are on tight budget book your train/ flight in advance preferably two months for best rates. Travel on weekdays preferably Wednesday and come back on Sunday.
Do the hotel booking in advance if your schedule is perfect. In Paris living in the center is not a priority due to the superb Metro network.
Try to locate hotel booking portals/ sites which do not charge for booking, hence there will be no cancellation charges if you change your plans.

Try the following sites,

• Etaph hotels belonging to Accor group, the hotels are cheap, no frill hotels/child friendly/no cancellation charges/no curfew(limit on entry and exit times).
• Venere's site also gives some good offers.
• Hostelbookers is another site which has some good offers.
• Hostelworld is also a good site and has a price promise on its web page of offering the lowest Internet rates.