When talking about the rule of threes and card making, I typically apply that to grouped items. If I'm stamping a few flowers for instance, I try to either have a group of three, an odd number, or in some cases, multiples of three. I have found that a grouping of 6 can work, simply because it's 2 groups of 3. Basically, it's just tends to be more interesting to the eye to work in odd numbers, especially threes.
Now, when I talk about the visual triangle, I usually refer to the actual layout or placement of elements. Any 3 points (there's that number again) can form a triangle, the shape of the triangle doesn't usually matter. I find that this triangle is achieved easiest by using similar items or colours. Something as simple as a black outline of an image stamp, a black sentiment, and some black ribbon or matting; or repeating a visual item, such as flowers in pattern paper, in your images, and in your embellishments. Once you start to look for these triangles though, you really start to see them everywhere!
The only problem with these concepts are that they seem overly technical and stamping is about the fun and the creativity. So try not to overthink it. However, if you come upon a design that just isn't coming together, step back and assess things. Once you get used to this idea, it starts to come naturally.
Okay, so here's my card. I went with some of my favorite paper and this fun font- it's a Quickutz die called Chocolate. Love it!
In case you are having a hard time seeing the triangles, or what exactly I mean by visual triangle, here's a diagram. I'm using the colour orange as my triangle/group of 3. You could even draw a triangle based on the vanilla items (the ribbon, the paper behind "you rock", and the background part of the flower).
Paper: Haiku DSP, So Saffron, Tangerine, Vanilla
Accessories, etc.: Chocolate Alphabet, Vanilla grosgrain