Keep in mind that in order to obtain something, you have to have a start.
That said, it honestly isn't too difficult if you understand the player value of cards. While a store may sell you something for 5 dollars or so, it doesn't mean a person is willing to trade that much in cards (value-wise). That said, it also doesn't mean that players are NOT willing to do so and you do find situations where you earn more in overall value than you would otherwise.
The biggest trick I found when I used to trade a lot was that the more cards with decent value I could obtain, the better. It sounds like an obvious statement, but there are times where taking, let's say, 3 VS Seeker over a Greninja BREAK is worthwhile. In certain regards, both even out in value (at 12 dollars), but I can potentially trade VS Seekers for more overall. Little things like that carry you a long way. Also, keep in mind that when you want to trade upwards, people are more willing to take more in Quantity than in Quality as a whole. After all, if someone is trying to build a new deck (which is pretty common), they'll most likely need Staples, meaning they'll want more of those and less of whatever they're willing to trade.
Finally, one of the biggest mistakes I feel people make when it comes to trading is...sadly, feeling guilt. When you want nice things, you (typically) have to be ambitious. I know it sucks and honestly, I'm not a fan of it either, but there are simply times where if someone offers you a good deal, you should take it. I'm not saying be a total jerk and attempt to intentionally convince younger individuals to trade their best cards for your bulk, but Business (and yes, trading is business) is sadly cutthroat at times.
Hopefully that helps. It can be quite a chore at times, but assuming you don't simply buy multiple packs or you don't simply spend a bunch on singles, this is most likely how you'll be obtaining anything of true worth when it comes to TCGs in general.
Take care~
-Asmer