Hands down, you'll have to memorize a ton of stuff in med school. The good news: you'll get better as the year goes on.
My most difficult time (albiet, I am only finishing my first year, so there are more difficult times to come) was studying anatomy. About halfway through gross I figured out a good studying techinque for myself. I'd pre-read the noteset, and as I came to a structure I didn't know, I'd find it in the atlas.
Now, I knew almost *no* structures, so every other word from the noteset had to be looked up in the atlas.
After finding the structure in the atlas, I'd look at what relationships it had to other structures, and it really helped me.
I did flashcards for about half the year, then when I had to cram I'd use 'flashcard-esque' techiniques with board review books. There's a lot of memorizing in biochem, too, but because many of the biochem pathways interrelate, it was a little easier for me to memorize them.
Again, as others said, repitition is key. For lecture to be an effective iteration of the repititive memorizing cycle, you should be prepared for lecture and make sure the new vocabulary words are not so new before you go.
Good luck - remember grades are relatively arbitrary and are no measure of your potential career