In my poetry, I usually focus on form at the level of the line, especially while writing and first revising. I focus on the line level first (after coming up with a basic focus for the content that I want to somehow communicate), because it helps me think in clear and defined images, and the line allows me to focus on how those images that I’m stacking up in a stanza intertwine and carry the content of the language I’m putting down across the space of the line break. I use line lengths to control both the amount of imagery and information that the reader comes upon at a given time, and to control the speed, the breath, with which the poem unfolds.
I use stanza breaks and stanzas themselves as forms of movement between tones or ideas, breaks for deep breath, or breaks for space and resonance (allowing an echo). I’ve always loved the idea of the stanza as a room (thanks Italy), though sometimes it can be a hoarder’s room or a crowded one room house–it’s a helpful metaphor for working through how I want each movement of the poem to feel, and whether that feeling lines up with what I’m trying to say.
I’ve thought about form on the level of meter, to the extent of trying to speed up or slow down poem by changing syllable stresses in the line, but I haven’t gotten to the level of picking a form to extend and enforce a particular poem that needs that particular form. I feel as though that’s the next step, the big step, toward controlling movement and pacing in the poem–putting it in a particular form that has been handed down, a sonnet, or terza rima, when appropriate, in order to really put my language under pressure, make it jump through hoops and perform the feats that will get across the ideas, problems, and particular descriptions I’m looking to communicate.