I don't have any specific advice for you other than what others have said, most importantly "don't be preachy, just write a good novel", but if you want an example of some incredibly based sci-fi, you should check out some of Heinlein's works on the off-chance you haven't already. Especially Starship Troopers - the parts where the protagonist explains the philosophy of his world are amazing and they're not preachy at all. The part about the guy who deserted and killed a kid really sticks with me, and overall, the depiction of a world where good men are driven by a sense of duty is just incredible - and again, it's not trying to convince you about anything, it's all presented as a matter of fact. (There's also one bit discussing the world "before", and it was eerily prescient back when the book was written, but it's not very judgemental either, the protagonist just talks about how he doesn't understand why people let things get as bad as they did.)

The Moon is a Harsh Mistress gets pretty based at times as well. Just... try to ignore Heinlein's weird obsession with polygamy and other weird relationship stuff.