This one's a bit obvious but watch your high school path carefully, besides good grades admission offices tend to look at the whole school record too and that includes activities you may have partaken in or clubs or some sort of organization, yes grades are still a big factor but seeing that you're also a social and active member of the community you're in is very well looked upon so don't just study hard, go out there and try things.

One other factor that's taken into account some places more than others is your work experience, either voluntary or not. Having a view on what lies ahead for your future, working with others and just have a little concept of what it is to work is very well looked upon because it shows you're committed to your future and you will work for it which can be applied to your future academic course. Besides that, having had a job previously may have opened the possibility for you to save some money for college, since tuition is always a concern, with some saving you could avoid worrying with loans, financial aid and other bureaucratic things to get you through university and frees you from future debt.

Talents and skills not that often are overlooked, if you have practical or relevant skills doing something make sure to let admission offices know about them, colleges and universities do tend to prefer individuals that stand out, mentally at first of course but so do they look upon those that can show useful or exceptional talents that stand out.

As part of the grades advice, don't slouch on your GPA's they exist for a reason, to get you into the university or college that you want to attend so prepare for them with enough time, if you spread your study through enough days you'll end up less stressed and much more confident of what you know.

These may not be huge advises but none the less they are advises and when it comes to getting into a nice, good place for you to get your future up and running, every advice should be taken into account.