You found them locally? Great. Golden Teacher (GT) is good.
The three major causes of contamination are:
Improper sterilization of the medium you're growing on. If you're using PF tek, you have to sterilize the jars. If you have a pressure cooker this isn't a problem. If not, you can still sterilize the jars but you should pay attention to the guides you read. Don't try to do it on your own. Boiling for example, is not going to sterilize the jars.
Most contamination is introduced during inoculation. When you are injecting the spores into the jar, you have to be VERY sterile and quick. The needle must never ever touch open air. If it does, use an alcohol lamp or cigarette lighter to make the needle red hot, then cool it down with an alcohol swab. Keep the needle covered with a soaked alcohol swab at all times.
An ineffective filter on the jar is the next reason most people get contaminants. If you've injected the spores without a hitch, make sure the lid of the jar is tight and make sure the filter you put on the jar is secure and works. Don't substitute! If the guide says to use tyvek or polyfill, that's what you use. A cotton ball or coffee filter is not effective for mycological work.
It might sound overwhelming but you really can't fail if you follow the guides.
