My first piece of advice is to get as much of the application process done as soon as possible. I had all of my stuff sent in before October and I can't even tell you how much better I felt knowing it was all done. I remember staying in one Friday night and cranking out everything so I could send my essays to my college counselor to read over Monday. Put in the time in the beginning of the year when you don't have as much going on - you'll thank yourself later!
Meet with your college counselor
I was fortunate to go to a small high school where we all got very familiar with our college counselors, but if you don't have an assigned advisor of some sort, I would suggest looking into meeting with one. I had a ton of questions about rolling admission versus early admission, etc and it was so nice having someone to meet with or email for a quick question.
Have someone read over your essays
I read over my essays several times (aka printed them out and went through with a red pen) and then had my dad and a few teachers read them as well. Going off my last point, have your college counselor read over your essays too! They're such a great resource and have tons of knowledge about what schools are looking for in an applicant.
Have a variety of schools
I applied to about 5 schools which was perfect for me because I was already pretty set on two (Indiana University and Miami University in Ohio). Even though I knew I wanted one of those two schools, I still applied to 3 more because hey, you only go through the college app process once! I know people who applied to 11 and people who applied to 2 - you really just have to find what's right for you. Also, make sure you have a few different schools in terms of difficulty of getting in. Have one or two reach schools, one or two safeties and then some more mid range ones. That's what my advisor suggested as well as what I found to work best.
Make a resume
Some schools ask for resumes as an additional part of the application and I definitely recommend uploading yours. From what I can tell, they seem to really help strengthen your application and are a great way to talk about other activities you do if they don't fit into another part of the application (ie. a unique club you're in, a business you run, etc.).
Get letters of recommendation
Pick two teachers or "mentor" sort of people you have good relationships with and ask them to write letters for you. Make sure they know you well and can talk about your strengths and areas of interest. I had one written by my physics teacher because science wasn't my greatest strength, but he knew how hard I tried in the class and how often I came in for study sessions, extra help, etc. The other one was written by my history teacher whose club I was also super involved in (he also knew about my blog and my interest in business so that was beneficial too!).
Meet with someone at a few schools you're serious about
Near the end of the decision process, I met with someone at Indiana and Miami to get more details about the programs I was interested in. It helped get my name out there as well as provide me with more information about the classes and opportunities each school had to offer.
If you ever have any other specific questions about the process, feel free to email me at email@example.com! I'd be happy to help you because I know how overwhelming it can all seem!
Any other tips to share? Comment below!