Similes and metaphors function differently in poetry; it's not simply a matter of choosing one over the other to save words. There is an immediacy and raw primitive power in the metaphor that is diluted by the simile's "like" or "as": it brings the symbol closer to what it refers to. But sometime you need the distance the simile provides you. We see this raw power of the metaphor in La Luna Asoma by Spanish poet Federico Garcia Lorca:
When the moon rises,
The bells hang silent,
And impenetrable footpaths
Appear.
If he'd written "and it's as though impenetrable footpaths appear" it loses much of its power, doesn't it?
Another example: W.S. Merwin writes in When You Go Away about the grief arising from what has gone unsaid to someone who has departed:
And that my words are the garment of what I shall never be
Like the tucked sleeve of a one-armed boy
Note that he uses metaphor in the first line, simile in the second but that are embedded in a rather complex metaphor: even the simile is part of the metaphor. A metaphor and a simile within a metaphor. There's more going on here than cutting out words to preserve the rhythm of the lines: it's a conscious choice on Merwin's part, and he knows exactly what he's doing. The simile inflates the grief of the protagonist's futile words into overwhelming tragedy, I think, and putting a metaphor in its place doesn't work because it performs an important function in these lines. Try this and ask yourself why it doesn't work from the perspective of what's being communicated in these lines:
And my words are the garment of what I shall never be:
The tucked sleeve of a one-armed boy
Not quite the same meaning, is it?
So choose the elements of your poetry carefully; if someone asked you of every word choice, every metaphor or simile choice, "why did you do it that way?" could you provide an answer that would convincing to them? To yourself?
A few other suggestions: many budding poets write a lot of what's call confessional poetry. This is hard to pull off well, since (frankly) no one really cares about someone's strong feelings - everyone has strong feelings, they're a dime a dozen. If you're truly serious about poetry, I'd suggest reading, reading, reading; find poets you admire and try to write something in their style. That will be a great education in and of itself. Read poets on writing poetry. Be your own severest critic: put things aside for six months after you've written them, then come back and either revise them or throw them away. Ezra Pound read T.S. Eliot's The Wasteland, took out his blue pencil, and reduced it from over 1000 lines to its final length of 434. Be a generous creator but a ruthless critic.
Here's some great advice in poetic form that W.S. Merwin received from his mentor, John Berryman:
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