I'm trying to learn the trading system as I'd like to be able to get more powerful cards and hp without spending tons of money on the game. Is there someone here who wouldn't mind showing me the ropes?
Trading in this game can be a bit complicated. There are so many factors but the most important one is WHY you are playing.
I play for fun and I will share my trading "strategy"
My basic rule is to determine what I ULTIMATELY get from the trade. If I come out ahead in the end, even bad deals can be good.
Card for card trades.
There are basic types of card/card trades.
First is the 1 for 1. This is the easy kind of trade. You can actually compare cards for the most part (ATK/DEF/Rarity/Cost etc). The one thing you can't compare is how hard the cards are to get. Two cards may have the same rarity but one may be an award for an event and the other is a quest reward.
1 for many trades are where one side gives up several cards to get a single card (or many just not AS many cards) from the other. These are slightly tougher to judge because the rarities and other stats can vary by card.
Card for Item trades
I don't personally do these often but you see them faily frequently. You can trade HPs, CWs or, rarely, MCs for cards. People who do this list their prices on their profiles or their support comments so just check them out and see if anyone has anything good.
My rule is basically to figure out if or how much a trade helps me. I've been known to take a "bad" trade because it got me the last card I needed to evolve something really good. Right now, I have a couple skull riders I will eventually get around to making use of but a lot of people seem to want them. The problem is that the offers for them are cards that I have/have had or no longer need. Good cards just nothing I need at the moment so I refuse the trade and hold on to my riders.
Another tip is to focus your trades. Check out the Wiki and figure out which cards you want. Then figure out how to get them.
Some can be had by getting people to join and use your referral code. Others by questing. Others by doing well in holy wars etc.