My friends and I teach people how to play at just about every social gathering I go to. One of the most interesting things I have found is that players are often significantly better when they are using a deck they find fun, maybe help them construct their own decks, finding out what works for them.
As for handicap rules, I don't prefer them, as they give an advantage that they may be reliant on in future, but I do have some ideas:
- All players play with their hand revealed.
This is especially good for teaching players, as it allows you to advise them on what to do next and to help them formulate strategies they may not otherwise think of with their current deck. It also allows for easier reactions to anything that may be surprising, such as counterspells.
- Provide a monologue of the current game and the ways it could go.
Admittedly, this can get tedious and annoying, but it helps players to further understand the effect from their triggers, casted spells, attacks, etc. By talking with them about the effects that their actions may have on the game, they can understand it better and in more depth.
On the subject of remembering rules and understanding cards, practise absolutely makes perfect. However, if you decide to do joint deck building, then consider trying to ease them in with more complex spells. The revealed hands can let you know when to help them (and gives an advantage for anyone with discard cards). The game monologue, by making all events obvious, can advise them on what to do next and helps to prevent mistakes.
That's just my two cents, have fun!