Teferi's Protection, Exploration, Mana Crypt, Revel in Riches, and Cryptic Command are just a few examples of cards - pulled right off the top of my head - that any random grouping of Commander players would, by and large, agree are "good"
By turn four or five, you should be seeking to go on the offensive with a lot of power at your back
For Marshal to get its full value, you need a creature to die before playing it
Even better, 1 in 20 art cards opened are gold stamped with an artist's signature or Planeswalker symbol
Attacking with Dragons draws you cards and can drop extra permanents for free, so combat turns into a steady stream of value instead of swing and pass. Focus heavily on early ramp and color fixing so the cost reduction matters as early as possible