Written by Tamika Bassman (Adapted by Prerak Juthani)
Also definitely go to GSI office hours because they will explain concepts in different ways than professors and can often boil information down to what's most important. Don't limit yourself to only attending OH for the GSI that teaches your specific discussion section, as there are often other GSIs you will find to be equally if not more helpful and skilled teachers.
In addition to what has already been said, I would check out this website: http://echem1a.cchem.berkeley.edu. It is essentially a bunch of short videos created by a Berkeley chem prof that cover a lot of what MHG covered when I was in his course (but the videos are just in less depth). They are a really good way to introduce yourself to the material and to review and test for your own understanding.
Also just FYI it seems as if Chem 1AL professors can differ greatly in their teaching styles. It is true I believe that most students got A/A- in fall 2015, but I had friends in Chem 1AL spring 2016 who told me that their professor said that very few people would get A's (he was grading on a slightly more brutal bell curve, I think) and that their professor had very calculation-heavy labs. So just be aware that Chem 1AL and its workload can depend heavily on the professor.
If the textbook is Quest for Insight by Atkins, I have one and am looking to sell (PM me).
If you work hard (and study in advance - kudos to you!) and take advantage of SLC/OH I'm quite sure you'll be just fine and actually get a lot out of MHG's class and your first semester at Cal!