uses only nine words, and usesalliteration and a variation on the word success to please the ear. Additionally, it contains a touch of irony or paradox. Only those who don't succeed fully appreciate success, according to the poet. 

The next two lines use metaphor and a version of synesthesia. Success is compared to nectar, but instead of referring to tasting that nectar, Dickinson uses the word comprehend. Synesthesia is type of figurative language in which what can be appreciated through one sense is described with another, such as describing flowers as melodious. Here, Dickinson uses the brain's ability to understand to mean "appreciate the taste of." 

The next two stanzas use analogy to illustrate the aphorism. An analogy is an extended metaphor. Dickinson uses a loss on the battlefield to show that the defeated party appreciates victory in a way that the victor cannot.

Stanza two also makes use of metonymy, which uses something associated with another thing to represent the thing. Here "took the Flag" is a figurative way of saying "won the battle." Obviously merely taking a flag cannot constitute a successful outcome in a war, but the figure of speech is used here to indicate the triumph of the winning side. 

Finally, Dickinson uses sound devices in this poem. She uses predominantly iambic trimeter rhythm and meter. Every other line rhymes. Alliteration occurs in lines 1 and 2 with the repeated /s/ sound; lines 3 and 4 with the repeated /n/ sound; line 6 with the repeated /t/ sound; and line 9 with the repeated /d/ sound. Assonance is evident in the first stanza with repeated long /e/ sounds and in the final stanza with repeated long /i/ sounds.

Dickinson skillfully uses figurative language and sound devices to convey her ideas in this brilliant little poem.

In this poem the speaker states that success is most valued by those who fail, just as victory in battle seems most precious to a soldier who is defeated and dying. Dickinson uses an analogy to state her claim in the first stanza:

To comprehend a nectar

Requires sorest need.

Here she compares a thirsty person's appreciation of a drink to a loser's appreciation of victory, saying that the thirstier you are the more you are going to value having that thirst quenched. In the same way, those that suffer defeat will crave victory more than the victors.

She goes on to use imagery very effectively in the last stanza to seal her case:

As he defeated - dying -

On whose forbidden ear

The distant strains of triumph

Burst agonised and clear!

Dickinson thus creates an image of a soldier dying on the battlefield (note the alliteration in "defeated - dying" which emphasises the pity of the soldier's state) who is nevertheless able to hear the victory chants and music of the opposition. He has just lost his life in vain and thus, Dickinson argues, is able to comprehend the nature of success far more than the victors.

One way to identify and analyze tone is to look at the writer’s word choice, which we refer to as diction. Emily Dickinson’s poem “Success is Counted Sweetest” is, like most of her poems, very brief--a mere 53 words. Dickinson’s skill as a poet lies in her ability to say a lot in the space of those few words. Let’s look at her diction and see what kind of tone we can identify.

Ne’er (the truncated form of “never”--Dickinson wanted to shave off half a syllable here), sorest need, not one, defeated, dying, forbidden, distant, agonized.

Here are ten words, almost 20 percent of the poem, that communicate the idea of loss and of being denied the joy of victory. When determining a tone it is important to remember that you’re looking for a word that that expresses the artist’s attitude toward his/her work. There is rarely, if ever, just one correct tone to a work, because there is always variation in the readers’ perception of the work.

I would say that the tone of “Success is Counted Sweetest” is mournful. It laments the “agony” (to use one of Dickinson’s own words from the poem) of those who suffer in defeat not just once, but always. But you, and countless other readers, might perceive a different tone, although all would have something to do with how it feels to "ne'er succeed."

It is difficult to find an absolutely upbeat poem in Dickinson's work because she focused so many of her poems on death and dying.  For what seems to be truly upbeat, you might take a look at "Wild Nights."

Even though the tone of "Success is counted sweetest" is not particularly grim, the sentiment Dickinson expresses is, and she sets the parameters of this poem in the opening lines when she says "Success is counted sweetest/By those who ne'er succeed."  And her first example is, of course, a hummingbird that truly understands the value of nectar when it is in "sorest need."

The second and third stanzas continue this theme of understanding the value of something, in this case, success, when one is in the depths of defeat.  Dickinson essentially says that victors in a battle really don't understand the value of victory, but the dying and defeated warrior who hears the celebratory trumpets of victory is the only one who truly understands victory--primarily because victory has slipped away.

In typical Dickinson fashion, this poem has a bitter-sweet component to it--true understanding of value comes with suffering. Also true to Dickinson form, the poem's matter-of-fact tone is offset by the grimness of the sentiment.

Dickinson also employs irony, created when what we expect to happen differs significantly, or is even opposite, of what actually occurs in reality. In this poem, the speaker claims that it is really the loser, the person who never wins or succeeds, who more fully understands what it means to achieve success or triumph. The speaker says,

Not one of all the purple host
Who took the flag to-day
Can tell the definition,
So clear, of victory! (lines 5-8)

In other words, no one can define victory as well as the person who has desired it but has never actually experienced it firsthand. The loser, then, actually comprehends what it means to win even better than the winner. Such a claim is probably the opposite of what most people would expect. After all, how could a person who has never succeeded possibly understand success better than someone who has actually experienced it? Dickinson seems to argue that the "defeated," who seems to have been "forbidden" a taste of triumph, is most capable of recognizing it.

In the final lines of the poem, Dickinson also uses a metaphor to compare the feeling of "triumph" to a song when she refers to its "distant strains" that may or may not reach one’s "ear."

There are several techniques in the poem.  The first is rhyming The words that rhyme in her poem are "succeed/need", and "ear/clear".  She also uses imagery in the last stanza (imagery is using the 5 senses to describe something).  She describes, "On whose forbidden ear/the distant strains of triumph/Break, agonized and clear."  She is describing the sounds of triumph very descriptively, which is imagery.  She also describes the army as a "purple Host", an image that fits with imagery.

Then, for figurative language techniques, there is a metaphor.  She compares people who appreciate success the most to someone who appreciates nectar because they are starving.  She says, "To comprehend a nectar/requires sorest need."  This enhances the point that she is making, that success often is counted the sweetest to those who have fought and struggled for it, and never tasted it.

I hope that helps!