Rule #1: The wind hates you and will always blow the opposite direction you want to go. That won't ever change. You can paddle into the wind at a reasonable clip in a real boat, the raft is just terrible no matter what. And yes, you can zig-zag slightly into the wind to make progress, its called "tacking", but just paddling is just as fast.

Sea serpents - they spawn in the ocean, mostly at night I believe. Don't go into the actual "ocean" biome, you can get fairly far just hugging the shores and shallows, depending on your seed.

Have backup gear, and some food ready to go near your bed. You're going to die a lot, it's much easier to be ready for it.