This video (on youtube) is worth watching for a brief intro do Inssider. The home edition will be enough for you to see what channels various networks are on and how the signal ranges overlap.
Click where it says NETWORKS. You will see the various networks listed on the left side. Highlight your network by either clicking with mouse or scrolling with arrow keys. Then press the S key so that a blue star appears next to the network name. This helps you find your network, if there are lots in your area.
Depending on the frequency being used, the graphs at the bottom will show the networks ranges, with your starred network being in blue. The rest of the networks will be yellow, red, grey depending on signal strength and when detected.
With signal strength, you are looking at a negative number. -25 is better than -69.
On the right hand side there is a box showing network name and a Link Score. The higher the link score the better.
With a 2.4GHz network, channel 1, 6 and 11 are the commonly used ones as they avoid overlapping.
I am not sure how to improve things - I think the key is to select a channel where there are not any other networks within say about -30db. So if your network is -25db, if others are -75db on the same channel they should be far enough away not to affect things too much, whereas if they are 35db, then they are close.
Try changing the channel of the network on the router, 1, 6, 11, and record what the Link Score is for each... then use the one with the highest link score.
Keep in mind that your wifi card can only see wifi networks. It can't see other things using the same frequencies. This includes cordless phones, baby monitors, security cameras, Bluetooth devices, Xbox 360 controllers... the list goes on and on and on. To see those networks you need a special USB device which costs quite a lot (example).