Here is a couple of tips about things you might not know about.

Making Money:

Crowns are the lifeblood of your character, sure, you can't go on elevators with Crowns, you can't craft items with Crowns and you definitely can't wear Crowns.
But they can buy you Crystal Energy which you can use to craft shiny, wearable Crowns.

Anyway, people are generally confused about how to make them quickly, so here are some tips.

Graveyards.

Graveyards have more monsters, it's easier to control spawns and skeletons are super slow and drop tons of loot.
Graveyards also have lots of Energy Gates, which usually have Red Boxes behind them. Meaning you still have around the same odds of getting a Sealed Sword or Antigua from them, as well as a good chance of getting super rare crafting materials.

Items that deal extra damage to Undead are also easy to craft.

Cold Iron Carvers and Silvermail are simple enough to acquire and both have 'Damage vs Undead: Ultra'.

Silvermail also has the added benefit of being Sentenza resistant, which makes it good for PvP as well.

There's no Helm that deals extra damage to Undead, but you can wear a Grey Feather Cowl with it for protection from all damage types for those levels between Graveyards. It also offers a Charge Time Reduction: Ultra bonus.
But it may be hard to craft. Anything with Normal Damage resistance is a good alternative, though.

Doing Graveyards won't offer up as much heat as Arenas, but you will get a fair amount of Crowns and items from Treasure Boxes in comparison to Arenas, for much less work.

So if farming is your thing, graverobbing is the way to go.

Alternatives

There are a couple of alternatives to Graveyards.

You can farm Arenas.
They're not as easy and if you lag, they can be intensely frustrating. But the variety in materials you receive, as well as the additional amount of heat make them more worthwhile to groups of players.
Tier 2 Arenas also seem to be the only way to efficiently farm Blast Powder, since only Ironclaw Demos seem to reliably drop them.
They also drop Unstable Cores, another semi-rare material.

The other way is to trade Crystal Energy on the market.
If you can buy it for less than what you can sell it for, you can gain a constant stream of Crowns without really having to do anything. It doesn't cost you anything if you buy the Crystal Energy and then sell it in the same bound, but offers up quite a profit.
This is something you can do while you're farming Arenas or Graveyards for Crowns.

Selling rares.
Items that are in high demand for crafting, will always be a good way to make money. If you don't need an item for anything you're making, sell it.
Dragon Scales, Sun Silver, Shadow Steel, Flame Souls and Meteor Motes always seem to be in demand.
Blast Powders and Unstable Cores, as well as Swordstones are to a lesser extent. Buy you will most likely end up using those for your own crafting purposes.
Making a thread in The Bazaar is a good way to sell items, whether they are in demand or not.
Recipes that are in high demand as well as premade items, also seem to be a good way to make money if you have the time. But often this is much more effort than it's worth.

You should experiment to find which one you find the most efficient, but these are the best ways I've found to make money.

Good item sets:

This is generally for the benefit of newer players.

• Currently, the title of best set in the game goes to the Angelic line of armour. It offers good damage modifiers, it has very high Normal Damage resistance and depending on what your final upgrade is, excellent defence against the Fire Status. Getting the Valkyrie Mail along with a Crown of the Fallen will give you about the Maximum Defence in both Shadow Damage and Normal Damage, with no negative Damage Modifier against Fiends, no Weakness or Resistance to Fire and a very high Resistance to Poison, while also getting quite a lot of additional damage. Although the Fallen Set is arguably considered the best, regardless of it's drawbacks.
• Then there are the more offensive and specialty sets, like the Dragon Scale Set or the Chaos Robes Set. These fill a niche, offering low Defenses, but offering excellent niche offensive bonuses. Using would offer excellent attacking abilities, but at a heavily reduced defensive capability, meaning you will rely much more on your shield and movement for protection.
• Beyond these sets, there are the average sets, like the Demo Suit, that offer excellent bonuses, but only to a specific weapon type. They give the bonuses earlier than the other sets, which makes them good for newer players. The Vog Cub Set, in particular, has been reported to have an invisible bonus to Movement Speed. Whether this is intentional or not is unknown, but it may be worth crafting the set for.

What you use is entirely up to you, people use a combination of these in the higher end play. There's not really a bad choice, but damage is usually considered better than anything else.

This thread is handy to read as well. It offers up some advice on good weapons to use.
Though, once again, there's not a bad choice when it comes to equipment, it's really all about preference.

If there are any other things you think people should know, post them.