What 'Understand Your Openings' Really Means

Preparation Tips:

1. It's OK to memorise - 'Understanding' doesn't come overnight, it requires experience. For instance, you play a line you've just learned but forget one move and end up worse. When you recheck the line after the game it should click, 'Ohhh that's why I needed to play X'. Rinse and repeat.
2. Comfort and Consistency - When preparing with an engine, it's often very difficult to understand why the engine slightly prefers move A to move B, i.e. there might be some small nuance 10 or 15 moves down the line. It's not realistic or time efficient to try and understand every slight difference in evaluation, instead when preparing, you should pick the move that feels more comfortable for you (the plans seem more natural) or fits in more consistently with your repertoire.
3. Don't miss the forest for the trees - This point doesn't get enough attention, but it's something I've noticed in most strong players. I'm talking about those who not only understand the lines they play, but are also familiar with the lines they don't play. Even top players forget their analysis from time to time, but very often weaker players will be like a fish on land after this happens because they've only spent time studying the details of 1 variation. The best way to avoid this is to stay curious and study lots of games in different variations, even if you don't intend on playing them in your own games.

Memorisation tips:

I'm by no means a memory expert but these are a couple things that have worked well for me.

1. When studying on a computer, make sure you drag the pieces yourself in each line at least once. This is more 'active' compared to the 'passive' way of clicking through the line. If you have a physical board, playing through on that is even better!

2. If you're walking/cooking/cleaning etc. try and refresh the lines in your head. This not only helps your memory but also improves your visualisation.