Where to start really depnds on what it needs. If you post a full set of test results on your fill water we can give you a better idea. For example, some fill water has VERY high TA so that would be the place to start, even before adding chlorine, IMHO. Ditto for very soft water, sometimes adding calcium is the place to start. After either of these get the pH in line and shocking is alway a good idea on a new fill because chloramines are often used to sanitize drinking water. Once the water is balanced (TA, CH, and pH) then worry about the CYA. You should be able to get enough of the balancing done within a day so the pool should not go green on you. If it does shocking will take care of it quickly or you can throw a few trichlor tabs in a floater duing startup to get a bit of chlorine in the water on a regular basis and add a tiny bit of CYA.