Play it safe, you dont need to attach parasites to have a sucessful build ive finished entire runs without picking up any parasites as artifacts are more than enough for positive effects. parasites potentially add syngery with the artifacts depending on the build but usually come with a handicap.
That being said try not to pickup parasites unless the negative effects arent persistant and are more or less controlled, for example one parasite specifically has a negative effect of ‘obolites disappear 1 second faster’ another parasite has one that is ‘suffer damage from long falls’ (you can negate the negative effects of these pretty easily imo as you can dash out of long falls before hitting the ground to negate the damage or in the other case simply play more aggressively which is actually quite beneficial) so in my case i would always pickup these two parasites if i came across them; pending the positive effect was something useful to me (sometimes it isnt).
And unless you are some god like player stay away from malignant items or chest unless you choose to cleanse them with ether, opening or picking up chests/items like this is the number one reason why people dont progress early on, dont take on extra handicaps when you dont have to, the enemys will challenge you as is so you don’t want to be running around with nuisance malfunctions that you have to fix. Also stay away from fallen scout corpses until you get comfortable with your play style and abilities, they arent mandatory for progression or story but are useful if you avenge the deceased scout as the reward is free ether which stacks all the way up to 30. Just beware that the enemy that spawns from the corpse will put up a fight so dont spawn it if you arent prepared for a cage match.
last but not least prioritize saving money for dmg up upgrades at the fabricators that carry it OR repair efficiency (repair efficiency is super undderated) if you can boost that stat, a small med pack will heal like a large normally would, but damage is always your best defense if you can fry enemys before they can even blink.
My suggestion DMG UP > Repair efficiency up > Protection up. When you unlock astronaut and childs watch those two items should supercede everything else if low on cash, but if you sweep the entire biome before fighting the boss or continuing to the next area fresh off a death, then you will always have money to buy things at the fabricators, save up and dont waste the money until uve located most of them so you know what kinda upgrades u will be working with to choose from in whatever biome youre in but i would purchase the ones i mentioned earlier before some of the others. Parasites you deem ‘bad’ can still be useful for collecting extra money if youre strapped for cash. If you locate the device that removes parasites in exchange for obolities you can load up on all the bad parasites and use the machine to take them off for money in exchange! This is best done after you have swept the entire biome for enemys (then you can make your way around and load up on bugs since you wont be fighting with handicaps on since everything in theory should be dead already and you plan to remove the parasites at the device before advancing to the next biome.) BE WARNED though this is not a useful strategy if you have a parasite(s) attached on you already that you want to keep as the machine will pick one to remove at random (you dont get to choose).
Theres really no wrong or right way and theres multiple ways to go about it, but that should help some if youre brand new. The main thing is read all item descriptions/buffs/negative effects and learn the game mechanics. RNG doesnt play as big a factor as you might think it does, the player really does control his or her own fate you just need to weigh the risk vs the payoff when buffing up and looting.