Before purchasing a signal booster you should ensure you are purchasing the correct one for your needs, this means looking at the band it works on, what strength you need, and if you have any need for multiple network support, for example if people in your home or office use more than one mobile phone network.
You will need to pick a booster than works on your mobile phone network, for example in the UK O2 is on the 900 mhz network, so you would need a booster that supports this band if you are with O2.
However, you may wish to think about purchasing a multi band signal booster if there are people in your office who use more than one phone network.
It is very important that you choose the right range for your signal booster before purchasing, to ensure you are getting one that will cover your entire home or office.
Most signal booster stores will offer boosters that start at 100 sqm coverage and go all the way up to 2000 sqm, so you will want to work out what area of coverage you will need.