Packet loss and weak throughput is often caused by weak antenna design. Good news: You can replace the built-in antenna of your router with something much more powerful. It's a bit of a hassle, but it may make the difference between a slow connection (or none at all) and a speedy line to your router!
Unfortunately, the laws of physics sometimes stand in the way of proper wireless bandwidth and signal strength (where can I file a complaint?). First of all, the distance between your router and the wireless adapter is a more relevant factor than you might think. Here's a rule of thumb: Just by doubling the distance between router and client you can expect throughput to shrink to one-third of its original value. A wireless repeater, which will set you back $20-$100, should boost your signal noticeably.
In addition to distance, the other wireless signal killers are the objects and elements that are in the way of throughput, namely water and metal. Water acts as a blockade for 2.42GHz signals, so it may be wise to get all objects in your home or office that contain any form of liquids out of the way (this includes radiators and flower pots -- no kidding!). Also make sure that metal objects are not in the way of your router and your clients: this goes for metal furniture as well as metal boards, tech gear, etc.
Keep in mind that smooth and shiny surfaces are prone to reflecting signals and thus either creating drops or massive signal problems.
Some routers are set up with their "Power savings" mode on by default. The goal: save a few milliwatts. Unfortunately, this commendable approach reduced bandwidth disproportionately. Although my trusty Linksys WRT610N router wasn't set up with unnecessary power savings in mind, I turned on its low power modes just to see the effects:If you value bandwidth over minimal power savings, check out the router's setting and look for entries called "Transmission Power" or various Eco modes. Turn them OFF. Also, do check if your router sports some sort of "Automatic" transmission setting. You may want to turn it off and go "100%" all the time.