Not so long ago, I started to use my accumulated STEEM on my SM account (and the liquid STEEM I generate on my actifit account), to hit the market and try to buy more cards that I need or want.
The funds run out very, very quickly, so patience is really a virtue here. :)
The other thing I've discovered about myself is that I'm not internally a trader, but rather a collector, at least on the SM site.
One might think: sell cards you don't use or focus on a deck only. Well, I don't. Maybe I do it wrongly, but I don't sell, and I try to build up all my decks (except one for dragon splinter for now).
Keep in mind those adjustments that are made to SM gameplay every once in a while.
What is everyone's last pick card can turn around and start being used with a slight adjustment, and vice versa. A favorite card, played by everybody, might lose some of its aura.
So, why not keep them all then? True, it will be a VERY long way up. Especially with no more external funds used for now. But I'll get there.