Open command prompt
Go to Android Sdk folder.C:\android-sdk-windows\tools
In command prompt type adb install apkname.apk
If you don' find adb command then
Download the adb.zip file which contains adb.exe, AdbWinApi.dll and InstallAgent(batch file)
unzip and copy these files to tools directory.
Below are the Steps to install Apk on Mac os Android Emulator.
Open Terminal
go to android-sdk-mac\platform-tools
type ./adb install myApp.apk
If you get any error while installing on Mac just restart the adb.Below are the commands
./adb kill-server
./adb start-server
Note : copy apk to tools and platform-tools directories on windows and mac respectively.