Once you have mtr installed, you can test your internet connection with any computer on the network, or internet. For example "mtr google.com" will show all of the computers between your computer, and Google's webservers. Not only does it show you the internet address of all of these computers, as long as you're running mtr you will see how long it takes a packet of data to transit this route.
Most notably on the right hand column, you want to see 0% packet loss. Under the ping section you want to see under 100ms, or 1/10th of a second latency, especially if you want to do something like Skype/video chat.
If the first "hop" is the problem, it's likely something in your house. If it's the second or third, or shares the same domain name as your ISP that is showing packet loss or over 1000ms (1 second) in latency, it might be worth a call to your ISP and see if they can fix it.
You might also want to try something like Speedtest for an online bandwidth test.