Let's say that you are already somewhat good at the science and math subjects, if not, brushing up on those would be a good place to start. However, I think that many students going into engineering lack practical knowledge in their fields. Going the extra mile in this category can be well worth the effort.
I suggest you start working on your own electronics related projects. There are many places you can start and there are two areas that can go quite well hand-in-hand: microcontrollers (mcu's or uC's) and basic analog and digital electronics. My argument here is two-fold. Having a good basic knowledge in these two areas will allow you to pay closer attention in class so that you can grasp and focus in the harder concepts when they are taught. This is kind of like having good basic math skills in math class. The better you are at addition, subtraction, multiplication, and division the easier it is to follow along with what is being written on the board during class. The second point is that when you go to build electronic devices in lab or for projects, you already have a basic working knowledge of how to read schematics, prototype on solderless breadboards and soldering of pcb's as well as researching the different electronic components through books and online resources. Again, this prior knowledge allows you to focus on the newer concepts being taught and applied.
There are a lot of great sites to get started but here are just a few:
Instructables,
WISC-ONLINE for the electronics tutorials (a table of contents from a basic electronics book can greatly help with the order of viewing these tutorials),
Make,
Nuts And Volts,
Arduino,
Parallax,
PICAxe,
Adafruit Industries,
Sparkfun,
Raspberry Pi,
Linux (ie.: buy an external hardrive and install at least one version of Linux without having to partition your main hard drive which can be risky),
YouTube, and
Datasheet Catalog.
There are so many projects to start with but it is especially important that if you start with uC's that you make an effort to grasp some of the basic concepts behind component choices when adding peripherals to the uC. One example is adding an indicator light to a project. This could be an LED and its purpose could be as simple to let the user know that the device is on or it could be some indicator to let the user know that the device is in a particular mode of operation.
There are a few things to consider here that fall under basic knowledge of the devices and concepts needed. Concepts: Current through this part of the circuit, forward voltage, and voltage drops. Basic knowledge of devices: LED forward voltage, LED forward current, power dissipation limit of current limiting resistor.
You need to know the forward voltage of the LED so you know how much voltage is going to be dropped across the resistor. You need to know the LED forward current because that is necessary to allow enough current to flow through this part of the circuit and not let too little current flow or too much current flow and blow out the LED or resistor. All of this information is in addition to the knowledge needed figure out how to program the uC to get it to do what you want it to do.
If there are groups in your area then I suggest having a look at them as there will be people there with a lot of knowledge that can be of help. Maker groups, hackerspaces and school clubs can be great places for people to pool their knowledge. There are also competitions at different levels of schooling and outside of schools which might give you more focus to your projects.