There are a number of protocols available, the TRIZOL method is a commonly used one, which we also have used a lot , some intro can be seen here http://openwetware.org/wiki/RNA_extraction_using_trizol/tri
First of all I think you need to specify if you are planning on extracting RNA from fresh tissue or from fresh-frozen paraffin-embeded tissue! Once you specify that it will be easy for you to google the protocol you want - there is a large number of commercially available options!
Second thing to keep in mind regardless of where you want to isolate your RNA from is to make sure you do it in an RNAase free workflow!