In all honesty, the way I did ochem (I got straight A's in ochem... a couple points away EVERY FREAKING TIME from an A+... not to toot my horn or anything!) was not to think about a mechanism in "steps", but to think about it in "goals" or in "chunks".
For example, if I want to get an amine attached to the carbon of an alcohol, I'm not thinking "okay, I need to oxidize this alcohol to a carbonyl, find a good nucleophile to attack the carbonyl C--oh wait, I have to find a nucleophile that I can turn into an amine somehow--I'll use HCN. Ok, now that I have HCN attached, I need to turn it into an amine... alright, I'll just oxidize that ho".
NO. I'm just thinking "Ok, I need to get an amine out of this. I've done this hella times in practice problems... LiAlH4/THF --> HCN --> LiALH4/THF --> BAM! there's my amine"
when you start to do enough practice problems, you'll start to see a bunch of patterns. If you want to turn A into B, you need to go through a series of 4 steps. Don't learn the individual steps as standalone steps. Put them all together and see what all 4 of them combined will get you. When you start thinking about mechanisms in "chunks" like this, it'll make things a whole lot easier. Instead of spewing out 18 steps when writing a mechanism, you'll be spewing out 5 separate chunks, and things will just come quickly/more naturally to you during the test. You really haven't learned that much ochem, even in a full year of taking the course. So, if your prof gives you practice problems, just practice those multiple times. Chances are, you'll be tested on VERY SIMILAR concepts... honestly, there's only so much variation that can be made in ochem.