Most of organic chemistry is based on positive and negative charges. Negative charges, consisting of electron-rich species called nucleophiles, are attracted to a positive charge that lacks or is deficient in electrons. Once you understand that simple concept, organic chemistry makes sense and is actually enjoyable. Knowing this concept will help you understand why an alkene will not react with an alkyne, but will instead react with a substance such as HCl. And why does an alkene not react with an alkyne? Because both are electron-rich species and are not attracted to each other. Remember, it is negative to positive. No negative to negative or positive to positive. Almost all the reactions in organic follow this basic pattern.
The people who believe the course involves memorization exclusively are the ones who don't comprehend the above concept and feel that all of the reactions don't make sense. They just memorize that an epoxide will react with an electron-rich species, a nucleophile, but they fail to see the reason why this is true. So, the point is, remember the charges concept.
As for other topics in organic, namely stereochemistry, which covers the spatial aspects of molecules, get yourself a pair of models for you to visualize the structures if you aren't particularly adept in your spatial skills. If you do not have models and have poor spatial skills, I suggest you assign R/S configuration to every molecule you are asked to compare to another and then decide the relationship between the two. You will know what R/S is once you take the course. Do not try to just look at the two molecules on paper, imagine them in 3-D, rotate them, etc... to figure out if they are enantiomers or diastereomers because you may make a mistake. So, your best bet is to go with R/S.
Other than stereochem, reactions and reactivity pattern form the foundation of organic and you will be fine if you remember what I explained above.