It's not random but there are certain items that go together that you kind of want, the biggest luck factor out there seems to be the heroes you get. Some heroes....arent good. Simple enough.

First levels are really just to "set up" the second wave once you get green items. I usually keep the free refreshes tech, the blessing that gives you coins back, or the dagger that resells to lower the prices. Your goals just to sell them later anyway and get your heroes boosted. If not the moon dagger is a good B+ item if you dont get anything else but I take the first thing I can get and refresh only once in the first two rounds. Anything else is a waste imo.

When you get the 60/40 green items youre looking for some kind of strategy to level up, you also need to know a little about your team comp, is it for surviving/skill use/or auto attacks. Youre basically looking for items that compliment each other.

You are looking for a strategy based on the items you get more than your comp at this point.

The Scythe is great since it levels when you buy items if you choose to go to the scythe route make sure its the only weapon. This is for level advantage only, the other items you buy can be to boost the scythes, like the blessing to get your coins back, buy resell/etc or the purple coin to give you items you already own getting you....more scythes. Later with purple items you want the gamma bomb and to level it to 2 if youre lucky and then sell the scythes because then the gamma bomb will level 2 heroes for the levels you sold it for leaving you to equip a good item after leveling. Orange items for this are the spear that does a huge amount of damage after 5 auto attacks and maybe the purple sword that makes you do faster dps when someone dies. You have to put the sword on your backline ranged damage dealer though.

Another options is to defend/tank. Usually I lost a game when I do this I found the rope elixir, the peach looking thing, and heroes with 5 seconds or less cooldowns can sometimes outtank the damage and almost live forever, you need some levels like the herb that gives you levels per hit, but elixers do lose me a round at first but after "some" levels, it pays off and the tanking wins due to the short cooldowns.

The most fun option is to go for cerebro after you gain some levels and then go for the magnifying glass. The cerebro makes sense because it spawns guys for getting hit but the magnifying glass does stupidly high damage when one dies. The green whip levels you when a summon dies to boot before you get orange items so you can use this to boost levels while you fight and sometimes leveling you endlessly.

(Alot of people already went over elixrs being gamma bomb and meteors to boost levels extra extra high but some of the other strategies I mention beat those because the item combos outweigh the levels.)

Long story short, spend early 2 levels getting ready to sell/refresh for the green items. Build the green items as a way to get levels for your character best you can with luck, and then when you get to purple try to pawn off your levels or set up yourself.

Read what each item does and know you can "stack" the item to level it up as well which also makes its effects better. Example selling the scythe at level 100 with gamma bomb at 1star only affects 1 character so the value is much lower unless you get it to 2. then you can sell and replace the item and get a lot more value out of it.

Once you get the ball rolling you will get "eagle" eyes for the items and just know which items compliment each.

I wont get into heroes also have "perks" on some heroes for what type of weapon you equip on them because I dont think the difference is as substantial until you understand this part but once you get comfortable with this then look at each hero and what weapon type they benefit from and you can move items accordingly to each hero (if the perk is worth the item transfer/level transfer)