I subscribe to the theory that the best knots are those that you can tie consistently well.

So if you're new to a particular knot, I think it makes sense to practice at home until you can tie it quickly and consistently. I've fished with some less experienced anglers who should have practiced knots more at home as they waste too much time on stream with knots. YouTube is a good resource, but I prefer AnimatedKnots.com.

I don't practice knots much anymore as I fish year round and stick with a few trusted basics -- perfection loop and blood knot for leader building (at home); triple surgeon's for tippet; and improved clinch for flies.

With regard to the blood knot ... I only tie blood knots at home using a Dennison Blood Knot Tool and generally with heavier material while building (or rebuilding) leaders. When I'm on stream, I'll use a Triple Surgeon's knot to add or replace tippet or just switch to a spare leader with a loop to loop connection.