>>7764239Iron Blooded Orphans is a good starter, if you want to expand then go on to Universal Century (main continuity)
U.C. in order excluding side stories.
The Origin
MSG (1979)
Zeta
ZZ (double Zeta)
Char's Counter Attack
Unicorn (lesser extent)
Victory (only if you want more U.C., little weird)
Turn A (far future, post U.C.)
Don't get confused about different continuity like IBO and U.C., they are completely separate.