^Allergy tests are always a good idea.
You should take just one to see if you are allergic to it. Otherwise, a dose of 120-180 is good for a first timer. Google opiate potentiation for some more ideas about how to extend the high. I don't recommend taking more than 2 grams of APAP at once, especially because the FDA sets the max at 1 gram and they want to lower it still.
Be careful with certain opiate potentiation methods that inhibit liver function, as they will cause you to feel less of the codeine's effects. (Codeine is a prodrug).
However, other opiate potentiation methods such as using DXM or sedating (first generation) antihistamines such as diphenhydramine (Benadryl), doxylamine (various brand names), chlorphenamine (Chlor-Trimeton), promethazine (Phenergan, Sominex), and many others work very well with codeine. Check out
this thread for more information regarding the usage of antihistamines with codeine. Again, most methods that involve changing metabolism of drugs should be researched beforehand, because some of them do the opposite to codeine. When it doubt, read through the whole thread.
This resource is also quite helpful and very in-depth.
Be careful with other depressants such as benzodiazepines, barbiturates and alcohol. If you're new to this, I recommend not using any depressants except for the sedating antihistamines.