Here's a pattern that start's like Trifoil but gets fancier. It took me a while to get the three circles even, but while I was looking at one of my first attempts a notion hit me. I added some loops and flourishes, and suddenly my knot was a flower. After playing around a while, I discovered the floral version actually looks better if the circles are not even.
So this is a win-win Celtic knot. If you get everything perfect, leave it be. If there is uneveness, go natural and create a flower!
The general tips apply-look over all the steps before starting, and practice (best on graph paper) before you use it in a zen. Note how the loops all come back to each other.
For this tangle in particular, give yourself space but stay small, lol. Don't draw a square and try to make them fit. But note that my initial curves are about 2-3 squares long. Otherwise, your knot will get too big and the circles will be difficult to keep rounded.
Most of all, don't stress. Let your tangle decide if it wants to be a knot or a flower.