Looking online, I see many tips about using TAPE to create nice
edges when needed, when you smooth the joint.
Are there any techniques for making an accurate line without tape?

If you use caulk labeled "water cleanup" (usually latex), you can
achieve perfect results every time using a bucket of water and a
sponge.

Good idea for bathtubs, bad idea when caulking baseboards over
hardwood floors or between windows and wood sills :-)

I've used the sponge technique in many situations and it works well. You
wring out most of the water in the sponge, so there's very little risk of
water damage or anything like that.

It works great when caulking against a painted wall too, like you might do
around a vanity top, or where trim meets a wall. I've used it when patching
a seam in a floor too. It's nice because it doesn't leave any caulk residue
on the wall, it only fills the crack.

However, WHY would you caulk against a hardwood floor anyway?

Anthony