As a college student, it's possible your professors never took attendance, or you were in classes large enough that no one noticed whether or not you were there. In the workplace, however, this mindset can be really damaging. While different companies have different cultures regarding attendance and tardiness, it's so important to prioritize being on time for your job. Even if you think no one will notice, the chances are that someone will.
Being punctual sends the message that you're serious about your job, reliable, and responsible. Assuming you can slump into work late on a regular basis and not be called out for it is a college mindset that is not likely to lend itself well to the workplace.
3. Not Dressing Professionally
This is another standard that varies based on your office's specific culture, but it's always good to dress as professionally as possible. What constitutes "professional dress" often depends on your field (and the sad truth is that women are often judged more harshly for their appearance in the workplace than men are, even though they definitely shouldn't be) — but whereas rolling out of bed and heading straight to class, pajamas and all, was acceptable in college, it mostly isn't once you're part of the workforce.
If you're unsure of how to dress, it's a good idea to look at people who share your position and see what they do: Is it business attire? Lots of neutral colors and understated accessories? Does everyone honor the casual Fridays in your part of the office? Whatever it is, especially if you're new, it's a good rule of thumb to fit in when it comes to the dress code.