Simple way: use online tool http://www.javadecompilers.com/apk, upload apk and get source code.
Procedure for decoding .apk files, step-by-step method:
Make a new folder and copy over the .apk file that you want to decode.
Now rename the extension of this .apk file to .zip (e.g. rename from filename.apk to filename.zip) and save it. Now you can access the classes.dex files, etc. At this stage you are able to see drawables but not xml and java files, so continue.
Now extract this .zip file in the same folder (or NEW FOLDER).
Download dex2jar and extract it to the same folder (or NEW FOLDER).
Move the classes.dex file into the dex2jar folder.
Now open command prompt and change directory to that folder (or NEW FOLDER). Then write
d2j-dex2jar classes.dex(for mac terminal or ubuntu write
./d2j-dex2jar.sh classes.dex) and press enter. You now have the classes.dex.dex2jar file in the same folder.
Download java decompiler, double click on jd-gui, click on open file, and open classes.dex.dex2jar file from that folder: now you get class files.
Save all of these class files (In jd-gui, click File -> Save All Sources) by src name. At this stage you get the java source but the .xml files are still unreadable, so continue.
Now open another new folder
Put in the .apk file which you want to decode
Download the latest version of apktool AND apktool install window (both can be downloaded from the same link) and place them in the same folder
Open a command window
Now run command like
apktool if framework-res.apk(if you don't have it get it here)and next
apktool d myApp.apk(where myApp.apk denotes the filename that you want to decode)
now you get a file folder in that folder and can easily read the apk's xml files.
It's not any step, just copy contents of both folders(in this case, both new folders) to the single one
and enjoy the source code...