What do you believe are some of the other major influences on developing our attitudes toward different things in life?

It is hard to answer this since you say "other" and you do not tell us what influences are already known...

To me the major influence in developing our attitudes towards various things is our family.  I am not saying that we end up believing all the things our parents do, but their influence surely affects us in ways that are both conscious and subconscious.

After that, the media surely influences us, depending on the extent that we expose ourselves to things like TV shows, advertisements, etc.

A third thing I will mention is peers.  This becomes more important as kids get to be of school age and especially as they move towards junior and senior high school.