Efficiency & Shares
There are three types of shares - valid, stale and invalid. Valid shares are the good guys as they fit all share submission requirements. Stale ones are the shares that were delivered a bit lately because a block solution was already found. Invalid shares are the bad guys. They have an incorrect mining solution, and they're a sign of something wrong on a software (or hardware) side.
So let's talk about improving your mining performance and increasing your efficiency. Let's figure out how to fight with stale shares because they're the most common reason why efficiency can be low. First of all, we need to lower the latency between the pool gateway and your mining rig. We recommend getting rid of Wi-Fi and switching to a wired connection because it is the most stable. Ensure that your mining software is up to date, and you're connected to the closest pool gateway. Also, we don't recommend buying the cheapest CPUs and networking equipment for obvious reasons.
Now let's talk about invalid shares. Technically invalid should not exist, and they indicate that you might have something wrong with your drivers and mining software. Also, there could be a bunch of invalid shares due to extreme overclocking.