I think one of the fundamental things that can make a game feel overwhelming while learning it (or even while playing it later) is a long list of “default” actions available to the player at all times. I was recently learning the board game Through the Ages (by the excellent Vlaada Chvatil) and was presented with this!
Note the long list of actions listed in phase 3 (I count 13!). The main problem I find with this is that it is hard for the player to compartmentalize all of these actions together, so frequently you will have to iterate through the list one by one, think about whether it’s a viable action to take, and then move on to the next one, comparing each subsequent action to each previous one in the list. If the list is long enough (and I would assume 13 is for most players) by the time you get to the end of the list you very likely could have forgotten your assessment of action #1!
So as not to harp on Through The Ages, lets look at another example from Android: Netrunner.
On the right you can see the list of default actions that the Runner player can take on each of his turns (limited by the resource “clicks”). This list is of a much more manageable size than that of Through The Ages, and there are some other benefits here as well. Drawing cards, gaining money, and playing cards from your hand (option 3 and 4) are very common game type actions, and easy to shorthand in your mind (there is no branching complexity in terms of gaining a dollar!). Another advantage is that the final action “Make a run” is fundamental to the game of Netrunner and done frequently over the course of the game, helping the player to remember it and develop heuristic shorthand about situations in which it might be useful. However, I would argue that that 5th action: “Remove a tag” is much easier to forget because a) it is not used very often over the course of an average game and b) it is not a core/fundamental/defining mechanic of the game.
Some takeaways about default actions:
1) Try to keep the list at a manageable number (7 is probably a good max).
2) Actions that are common to lots of games are easier to remember (drawing cards, gaining money)
3) Actions that are inherently simple are easier to remember (gaining money)
4) You can get away with a few more complex entries, if they are fundamental to the play of your game and/or used very often!