Hi Triple,
I'd like to add to the fine posts posted here already...
I dont know where you stand academically, so it's hard for me to say exactly
what is best. I can tell you one thing though, that algebra will get you pretty
far along any of the roads you choose from here. Unfortunately like i said
i dont know how much math you have already had, but math is the underpinning
of much of electronics and mechanical engineering too.
Also, learning electronics alone is not like learning other things in a way, because
what you learn in electronics (resistors, capacitors, inductors) can be immediately
applied to mechanics (as robotics). For example, you can model many mechanical
systems using electrical networks, so if you know something about electrical
networks you are a short jump to knowing something about mechanical systems!
Pretty neat huh? There is just a simple translation of notions of how capacitance
converts to mass, and stuff like that. You can model a spring, mass, damper
system with an electrical network of a resistor, capacitor, and inductor! Both
systems behave the same except for what the electrical quantities represent.
So to start with, learn algebra if you dont already know that, and then as much
as you can about the theory of electrical networks.
If i had to say only one thing though, i would definitely say ALGEBRA !!
Of course have some fun in the process