I went back to school at 24 after six years in the military, so your mileage may vary, but starting out was tough for me. My peers were mostly fresh from HS and the prerequisite coursework was fairly fresh in their minds, but not in mine. For example in HS I had taken up thru Calc II yet going back I struggled to recall the finer details of algebra, and my alma mater didn't offer anything below Calc I. That forced me to get really serious about studying, pull some long hours in the library and with tutors, and ignore my social life long enough to play catch-up. I did it tho, and by the end of the first semester school seemed easy enough that I asked my advisor for an exception to policy to take extra classes. My first semester was the only one with 18 credits, somewhere about semester 3-4 I discovered that we could test-out of easier gen-ed classes early, and one semester technically took 30-odd credits. I graduated in three years fairly easily, 28 credits beyond the requirement due to poor scheduling of the final required class.
My best advice - Focus on getting assignments done as soon as they are assigned. I vividly remember that the odd bits of work/studying which I put off until the last minute always seemed infinitely more difficult than the stuff I did right away. Secondly, use the school's tutors and teacher's office hours to ask questions and solicit feedback, even if its simple things like asking, "Is this good enough or can I do it neater/better/more thoroughly?" Third, find a brief distraction that you enjoy to break up studying which won't develop into hours of waste. For me, whenever I started to struggle and needed a break I either went for a run or hit the gym. 30-60 mins later and my body wouldn't let me keep going, I had to go back to studying. Had I broken up studying with TV or gaming then I'd lose hours screwing off like some classmates who struggled.
Good luck.
