Now I assume that you use the Firefox web browser and have already installed it. If so follow the below procedure...
1. Now its time for you to download and install this addon for firefox called the GreaseMonkey (click on the blue text).
2. Then restart your web browser and click here to install the Emoticon script (it's ok, its safe - no kidding here).
That's it. From now on when you use the blogger post editor you'll see a bar of emoticons on the tool section and whenever you want to insert one simply click on the one you want and you're done!.
So that's how you can add emoticons in blogspot posts folks. Hope this did have some value in it. See ya!