WiFi performance can vary a lot depending on the brand/model devices that are connecting with each other. Your WiFi router settings will also impact how well your device can connect. Other factors include which band you are using ( ie 2.4 vs 5 ) and how crowded the channels are.
Start by using a util such as WiFi analyzer to see how busy the area you are in is. If you are using a 2.4 Router, likely it is crowded. Try switching the router to a channel with less traffic on it. In my area, the 2.4Ghz. has over a dozen other wifi spots shown and getting a clear channel is almost impossible. On my 5Ghz band... I'm the only one at this time.
Next check what settings your WiFi router has available and then look up what the optimum settings are for an Android on your make/model.
Everyone mentions ( and should already know ) that being too far away from the WiFi router can impact performance. I often get clients that have their router on one side of the house and they can't get a good signal on the other... this is normal but should be avoided if possible. What people don't realize is that being too close ( within 3-6 foot ) also affects the signal causing it to be overdriven which also affects performance. Think of it like when you turn up your stereo or home theater too much and overdrive the speakers.
Look for other sources of possible interference... wireless keyboards, mice, cameras, cordless phones and many other wireless devices often use 2.4Ghz frequencies ( but different channels ) so make certain these are not close by... set them at least 3-6 foot away. Since they are on different frequencies ( channels ) in the 2.4Ghz range, just getting some distance from then is all that is usually needed to avoid interference.
Other electronics can also have a similar effect if they are close by... house fans are notorious for thowing out interference on many frequencies. Of course TV's, monitors, computers etc should also be considered. Again, just keeping a little distance is all that is typically needed.
The other things like the types of walls between your device and the router can affect your signal. A steel reinforced concrete wall is nearly impossible to get a good signal through where just drywall and 2x4 construction doesn't impede it much as long as the distance isn't too far.
