1) Mechanisms

Some of the mechanisms are more important to know than others. Although it is wonderful to know all of the mechanisms from your textbook, you should especially concentrate on:
- the addition of a molecule across the alkene double bond. Know the explanation behind Markovnikov orientation.
- the substitution and elimination reactions that your book spent a whole chapter on were covered in depth for a reason. They are a great introduction to the electron-pushing style of drawing a reaction mechanism. They are also a good introduction to some three-dimensional issues with reaction mechanisms.

2) Memorizing
You're going to need to memorize quite a few reactions.I recommend making flash cards and reviewing these flash cards daily. I don't know any other way to keep all those reactionsinyour head. You need to have a rapid, facile command of ALL the reactions simultaneously for doing multiple step syntheses.

You need to understand the organic reaction process practcally so that u can that feel the essence and you can get the gist of it. For instance making the question yourself as why would the reaction talking the prescribed path and what’s the role of catalyst and about mechanism of the reactions etc. So practical knowledge will helps u alot and you can also check the reactions videos online so that u can get out of that byhearting phase.