Few things you urgently need to know, even though I'm far from an expert at RA2:
Never build to the max height. Even though it will give you more strength, it will also give you more weight and make your bot harder to control.
Never use casters, unless you want to completely cover your underside to protect it from
Pop-ups.Build to the weight limit. So this means make sure a lightweight robot weighs around 245kg, a middleweight around 395kg etc because no matter how efficient you think your bot is, it can always be more efficient.
Align any spiked weapons. Seriously, it looks neater and you can build some really mean robots with it, like this one:
Make your robot invertible or with a srimech. I bet anyone on this forum could KO your robot in less than 30 seconds with a robot they built in 2 minutes. All because there's no way that robot can flip itself back onto its wheels or drive upside down.
Only use rubber wheels or shiny hub wheels. They have the best weight efficiency of any wheels in stock RA2.
Make sure you're able to beat any stock AI opponent with your robot. Even Tornado, Raptor and Emergency. I know people who have built lightweights capable of KOing those 3 "deadly" heavyweights.