If you are trying to grow your SP, then powering up all STEEM is the way to go. For any SBD, you can trade for STEEM on the internal market (link in the main menu as well as your wallet). There are zero fees for this.
Regarding trading SBD for STEEM, you can just trade at the current market price, or you can try to time it and get the best value. If you watch the prices of STEEM and SBD, you get the most STEEM if you wait until the price of STEEM is lowest and the price of SBD is highest.
Thanks for this helpful advice, @timcliff. I'll take it. I'm also trying to earn more of anything by entering contests that have awards for the best entries. This seems like a good way to publish, engage and interact, and improve myself at the same time. Cheers!
I'm not sure how many of these are still active, but you should check out this post:
https://steemit.com/contest/@timcliff/looking-to-earn-some-extra-steem-sbd-check-out-these-contests-awarding-steem-sbd
Cool! Thank you so much, @timcliff! I'll do just that! Cheers!