For sure just run the barrel boards, forget the bottom hammer. Like Dave said, steer any and all barrels out of your way. Looking up 1 or 2 girders, seeing what's coming, and steering them out of your way will help you a lot.
Play safe. Don't rush into any situations. Think of this game like chess. You will survive longer and boost your scores if you are always thinking ahead, being cautions, and playing smart.
It'll always be better for you to stay put, or wait for a better opening...than rush into a difficult situation.
Fireballs in your way on PF screens? Wait it out at the bottom. An opening nearly always presents itself. Again you'll see these openings if you're learning to look ahead and recognize when you'll be safe...or put yourself in danger.
Rivets, do the star pattern...and learn when to abandon it if you must. Once again this requires thinking ahead! Understanding how fast the firefoxes are and when you can outrun them, when you're safe to get that hammer, when to wait on a ladder so a Firefox moves down and out of the way...it's all thinking ahead and playing the game like a game of chess.
Watching an expert play DK may seem like it's a simple game...and in a way it is...but what most people don't understand are all the things experts are doing, or not doing, on purpose...as part of a strategic thought out plan.
This game isn't popular just because its the first Mario game, or because it was in a popular documentary (ok that had a lot to do with it), but it's a gigantic mess of a math puzzle...which is what keeps us playing it...it's challenging and always different every time you play it.
Watch people's streams and don't just watch...think about what they're doing, why they're moving here or there, and try to predict what they're going to do next. Odds are it'll be something different that what you were initially thinking...and then you'll think about why, and hopefully learn from critically observing the gameplay of others.