I like to take a legal pad and a pen and go through each planet in my home system and sort of take inventory of what I have tons of. You can only have one command center per planet so it's good to come up with a plan for which minerals you will be extracting from which planets. If you're unsure of what to make, have a look on evepraisal and punch in all of the different possible T1 materials you can produce. You could also see if your alliance is looking to purchase certain products and you could tailor your production to suit.
At the time this screenshot was taken, I was after Microorganisms, which get refined to the T1 product Bacteria. The example here on J223650 II will be used for the rest of the guide.