Since 
First call, a friend says that internet is slow on his computer and that he can't get full speed. He had called his provider and the techinician was there, tested the connection with his tablet and he had a full speed. I asked does the connection works on his phone and he said yes. So then I asked him how far away is his router from his computer. He said half a meter and I said go and find a LAN cable in the box of your router and connect those two with it. After that the connection had full sped.
Today i went to my ex coleague who is retired to help him with his computer. When I sat down I noticed that the connection is slow. He has a 70/10 Mbps connection, and he could get only 10/2 Mbps. His computer is stuck in his desk, usb wireless card inserted ih back usb port and the router is two rooms away, also in some kind of a cupboard.
In the first case the router was to close and in the second one was to far away, and even worse it was between a couple of obstacles in this case walls and desks.
Wireless connection needs clear path between router and the computer (or laptop or anything else you are using) so the positioning of the router and the computer is the most common mistake people do.
Don't put your router in cupboards, behind objects, on the grond or somethng like that. He needs to be clear of all interferences and try to put the router as high up as possible to extend the broadcasting range of the radio waves.
If you are going to use wireless card on your computer don't put computer in tables covering your wireless card and don't expect perfect signal couple of rooms away. Materials like concrete and metal tend to be the worst for blocking Wi-Fi waves, but even objects of other materials can get in the way of high-performance wireless.
OK. We solved the biggest and the most common problem of wireless and that is visibility.
The second problem is the equipment. Make sure your wireless card is not older and out of date. Make sure you have all the updated drivers. Make sure that you don't have any other devices that can interfere with your router. Check your wireless card specifications. If it is older you probably will have to replace it. Sometimes you will need to check your router properties. The transmision power of the router should be set on high.
If you have many rooms in your house maybe you'll need to add an extra router ad set it in repeater mode. That is the mode when the second router copies your main routers properties and spreads signal further.
Another way of strenghtening your signal is buying high performance antennas, either for the router or the wireless card, depends which is easier to implement.
Wireless cards in laptops are also removable. If you have a slower card in your laptop it can be upgraded and it is not that big of a deal. Any trained technician can do it. If you are having trouble getting full internet speed on your laptop, check your wireless card, maybe you just need a higher performing one.
You can check your internet speed at http://www.speedtest.net/. If the results are far away from the speed you agreed with your interent provider try some of this solutions.