Do not get to expensive levels on decos till you unlocked base cost and plus shares. I am not an expert in particular, but this is not the first "Clicker" I have played and I see the math and understand the implication of spending resources and what I will get for it.
Rather unfair in this game is the randomness of the decos.
So my 2 cents for decos and skills. I assume playing with keyboard mouse or fast burst clicking for a minute. Strict idle is worst. Offline is far better once you have the skills/decos. And clicking on a private show is best.
If you will not at least click a minute or two between offline times, all the skills and decos improving your clicks are of course not worth as much to you.
Skills Priority
Collect All Private Shows
Tapping Coin Power
More Private Shows
Offline Revenue
Booster Time
Mega Coin (Spawns too seldom)
Decos (not ordered)
Stock Market
Now Useless. Was needed if you accidently hired the most expensive girls. Max is 6.
Neon Sign.
More Shares. You need this. Very expensive to level.
Sex Toys.
Level Cost Reduction. You want this. Very expensive to level. Works in addition to base cost.
Urn.
Company Multiplier. I do not know how this combines. Gets past 26.
Trophy.
Reply Timer. Seriously? Useless.
Music.
Upgade Cost. Max -26%. Nice to have.
Lamp.
Prestige Power. Gets past 26.
Poster.
Starting Money. Why? Useless. Gets past 26.
Sports Equipment.
Tapping Power. Added to the skill of same effect. Max +7.75
Drink.
Booster Time. Meh. For longer sessions. Useless for a speedy sell. Probly combines with the skill. Max +1.56Ks Time.
Couch.
Base Cost. You need this. Maxes out at -52%
Statue.
Key Drop Rate. Very expensive to level. Dubious Percentage. Is it added to an unknown percentage? If so, you need this.
Cabinet.
Offline Revenue. Added to the skill of same effect. Max +6.5
Plant.
Private Show Spawn Time. Maxes out at -26s
You should level all decos for their prestige as long as they are cheap compared to the decos you need, want or use most. Most impact has the base cost reduction. At the time I was writing this, I was somewhere around company level 160. Most decos are maxed and the ones that are not will take me several company resets for the next level and will improve me by almost nothing.