Hi
I use a recipe thhat requires 1 part cream to 2 parts chocolate (250ml cream = 500g chocolate)
Use can either heat in the micro stirring every few seconds or on the stove over a double boiler.
The smaller your choc pieces the quicker the melt and mix.
Good Luck 
I use Chef Taz's recipe and omit the sugar (granulated) it comes out alright depending on what kind of chocolate I use. I heat the milk in microwave, pour over choco let sit for 5 min. stir, then refrigerate for an hour if I am going to whip to use as icing and pipe with it, otherwise I just let cool outside of fridge then pour on cake or dip cake balls in.
I've used choco chips, bakers choco, candy melts,milk chocolate, what ever I can find. Not a big selection in my rural area it all works.
Here's an ultra easy, and ultra fast never fail ganache recipe for you:
1 bag semi-sweet chocolate chips
1 bag milk chocolate chips
1 pint heavy cream
1 teaspoon pure almond extract
Combine Cream and chocolate in a large saucepan. Heat stirring constantly, until chocolate is melted and mixture is very smooth and runny. Remove from heat and add extract. Pour over favorite cake.
Make sure you do this with your cake on a cooling rack over a jelly roll pan. Any excess can be pressed into molds for chocolate flowers or the best tasting fudge ever!
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