how do i get a higher chance on invading planets

artifacts that buff (increase) your attack. choose your targets carefully...if the planet has lots of defensive structures on it you probably want to look elsewhere.
what level are you at?

Get your attack as high as possible buy equiping the best weaponry you have and using whatever offensive artifacts you have (attack increases or ones that lower the planets defence/attack.) cloak isnt included in the overall invasion i think.

I try not to invade a planet unless my attack is X1.5 the planets attack and defence added together.

So if a planets attack was 500, and defence was 1000 over its planetary defence would be 1500 (i think anyway), not including planetary defence only structures.
either way i wouldnt attack unless my overall attack was 2250 or more.

highest chance of successful invasion is 90%, your ship attack power must be double the planets defence + attack + invasion defence + legion bonus in order to score a 90% success chance.

artifacts like
- crimson obelisk
- crimson amplifier
- ancient crystal foci
- mutagenic cartridges
- stryll pathogen
- special weapons : lazuli mind controller, psionic amplifiers

all can help in a planet invasion, its a good idea that you get 8x of your most advance weapons and activate those artifacts prior to an invasion