My only pieces of advice I can give for undergrad students who are looking to applying to grad school (all from my personal experience for this application cycle)-
Start kissing ass. NOW. If you haven't already, which you should've been doing a long time ago. Whatever you do, just keep hovering over professor's offices during their appointment hours. Go in even just to talk about something you discussed during lecture earlier that day. Maintain relationships. I cannot stress this enough. Go before submitting papers, after submitting papers, whatever. Some may say this comes off as annoying but it actually worked SO much in my favor, I can't even begin to describe to you. I was literally one of those kids who damn near lived at a teacher's office hours before a midterm, after a midterm, before a final, and after a final. I did whatever I could to get whatever extra help I needed, and to let teachers know what a great job they're doing and the positive effect they have on me. I have absolutely no regrets maintaining great relationships with professors. They are literally there to help you, that's part of their job. Some may be too busy but most not too much, at least they'll be there to help you with grad school questions. And furthermore, it's a great way for you to stand out in all the upper div courses they're teaching. I imagine it's hard to keep track of a lecture hall bustling with students, and it's up to you to decide how you want to stand out. You want a LOR writer who's going to showcase your performance the best way they know YOU. My past professors who were also my LOR writers for this season's applications were all too happy to help me out, to talk to me, to go over my SOP's, writing samples, the works, in addition to writing my letters. I was also really great buddies with a TA I had twice during my undergrad career, and she too looked over my SOP drafts multiple times. You have no idea how much is at your advantage when you maintain relationships with your teachers.
Really question yourself and see if this is what you really want to do. I know this sounds cliche but I know a lot of people who started questioning why they were doing this (AFTER they started the program.) It's really tough. You've heard it all..."don't try to go back to school to avoid the real world" but you have to really know what you're signing up for. Don't do it for anyone else or because that's what your parents expect. Do it because you have your own reasons to do it. That's all I can really say. Some may disagree with me, but this is just from a personal standpoint that I have reflected upon for the past 8 months.
For GRE, use Magoosh. I swear by it. Don't bother with those extremely expensive Kaplan or Barron or Princeton Review courses. They dumb down the GRE in my opinion, and I learned it the hard way. I'm happy to vouch that the second time around before I took the test again, I used Magoosh prepware and I improved my score by 15 points.
And as everyone's reiterated so many times on here, DO NOT PROCRASTINATE. Do NOT. I repeat, DO NOT. Have everything done early. You should have already looked at schools around this time of the year and spring into summer is when you should be going through several drafts of your SOP and writing samples. Don't ever send in a raw paper ever. Have all your materials ordered on time. I had a nightmare rush express mailing transcripts and GRE scores to my institutions. That was effing TERRIBLE. That's just more added stress you really didn't need.
As difficult as I know this may be to all of you, stay the HELL AWAY from GradCafe from December - April. I mean it. I MEAN IT. It won't do anything for you, all it'll do is freak you out. I know that being on here helps everyone come together to talk about their stresses and such which is great, and I love the Literature/Rhetoric community on here because everyone is so helpful and reassuring (and it's great that we can all either cry together or celebrate together) but just step away from the computer. Go outside. Get some fresh air. Being on here has stressed me out more than it has helped me sometimes, as much as I hate to admit (because I love everyone here.) Just don't go on the Results board. Don't go on any forums. Don't go anywhere near this place. I've lost a countless hours of sleep just from stalking the forums on here that just added to my stress. I'm telling you, it doesn't help.
I know these are very general pieces of advice that have been circulated for seasons coming but from my personal experiences from the past year since this whole application process has started, these are the steps that I really really cannot stress enough. I don't care if it's cliche, it is the TRUTH. I know there were things that I didn't follow that I'm stating on here, and who knows, there could've been better ways I have prepared but I'm happy with the outcomes.