The speaker starts out right at the beginning with a switcheroo. She makes it seem like she's starting an epic poem, but then she backs off. Apparently she's not going to write about "Wars…and…Kings" (1). All that is just too grand for her lowly, insignificant ("mean") writing. This starts us out on a pretty traditional note. Basically the message she seems to be giving is, "I'm not good enough to tackle 'superior' subjects." Well, we'll just see what happens to that…
Let Poets and Historians set these forth. (5)
She'll leave the big topics like politics and war to "Poets and Historians." (Well, actually, she won't—the book that this poem opens is full of that kind of stuff, but never mind.) What she's saying here is essentially, "Don't expect too much, I know my place." With a lead-in like that, you pretty much know there's a mighty big "but…" coming. Sure enough, with the beginning of the next stanza (7) she shows us that her ideas about literature and writing are way more complicated than this.
Great Bartas' sugar'd lines do but read o'er (8)
We just love this moment. It's such a great description of the joy she takes in writing and literature. Her favorite poems are just like candy to our speaker. It's clear, from this moment on, that we're dealing with a woman who loves and respects the craft of writing, and wants to do it as well as anyone (even if she worries she might not be able to).
A Poet's Pen all scorn I should thus wrong, (27)
This is the kind of crap she has to put up with. She feels like no one thinks that she, a lowly woman, can do the hard work of poetry. She's writing against a stiff headwind here, and she makes us feel all the pressure of prejudice in her society. Our speaker isn't exactly a rebel, but she's definitely ready to point out people's prejudices.
And oh ye high flown quills that soar the skies, (43)
Clearly our speaker has a deep respect for the great poets of the world, and she's too modest to even begin to compare herself to them. Here she makes them soar like eagles in the sky. Still, as we've seen in other places in the poem, she has a kind of mischievous streak and, for all the respect she has for poets and poetry, she relishes the chance to raise her voice (at least in writing).