If your gear isn't very good and it's too much of a hassle to trade for better stuff, use vendor recipes.
http://pathofexile.gamepedia.com/Vendor_recipes
What you do, is you take the required input items, and sell it to any vendor. Instead of the usual currency scraps they give you as return, they'll give up a slightly-upgraded item. For example, if you take a bow (try to find one with the best base damage you can), along with a yellow rustic sash and a blacksmith's whetstone, you'll get back the bow with its affixes replaced by "50-69% increased physical damage", which might be better than whatever weapon you're currently using.
The really useful ones are the % increased physical damage (or x added physical damage, if you have multiple spare granite flasks) for physical attackers and +1 fire/cold/lightning gem for elemental spellcasters. The movement speed for boots is also pretty nice.
I would also suggest not using orbs to just randomly roll items until the itemlevel of such items is 60+, except for jewels where the itemlevel doesn't matter (I personally wait until 75+) because the itemlevel of an item affects what possible things can roll on it. The higher the itemlevel, the better the affixes that can roll. The same orbs can get you much more if you put in the effort to trade.
As for currency rarity, I can provide a general overview:
Scrolls (Wisdom/Portal), Armor scraps, blacksmith whetstones, orbs of transmutation/augmentation/chromatics/jewellers/alteration are pretty common.
Orbs of chance/fusing/alchemy/scouring/regret, Glassblowers, gemcutter prisms, and vaal/regal/chaos/blessed orbs are less common. The chaos orb is the most commonly used bartering orb, and most of the others are considered worth a certain fraction or multiple of chaos orbs.
Divine orbs and exalted orbs are the rare orbs. Exalted orbs are commonly used when bartering for more rare/expensive items. You most likely want to save these to trade and not to craft, unless you really, really know what you're doing.
The mirror of kalandra is super duper rare.
In your search for 4 or 5 link items, have you regularly checked the armor/weapon vendor in town? 4-links should be pretty common after you've progressed somewhat through the game. They're also supplied as quest rewards in the later difficulties. 5-links are much less common though, let alone 6-links.
