I started by smashing N-back games, along with mnemonic training (remembering long lists of numbers), on daily basis.
I think the above helped by strengthening my willpower to endure substantial confusion caused by mental exercise (this kind of confusion is similar to when you try to learn something new from nothing).
Along those exercise I were reading books and programming (which I'm still doing to these days).
I'm currently meditating as much as possible whenever and wherever I go and while I do pretty much anything.
My meditation is just avoiding having thoughts, focusing on my breath and staying focused as much as possible on the here-&-now.
I'm opening a thread to speak about my experience with meditation.