i did an essay plan on negative capability and these are some of the points i wrote:
-'ode to a nightinglae' ends in an open way, 'Do I wake or sleep?' this shows that keats is in doubt. he is in a double-mind state, negative by being weighed down with thoughts of his death, illness and depression, but positive, by being reminded of the good things in life, such as wine, music and happiness, both at the same time. (you can use small quotes to back up this-eg. 'beaded bubbles winking at the brim'-presents his light, happy mood whereas 'my heart aches and a drowsy numbness pains'-presents his down, depressed mood)
-'The only way of strengthening one's intellect is to make up one's mind about nothing-to let the mind be a thoroughfare for all thoughts. Not a select party' this quote comes from his letters and backs up the idea of negative capability.
-'Negative Capability, that is when man is capable of being in uncertainties. Mysteries, doubts, without any irritable reaching after fact and reason.' also a quote from his letters.
-keats was inspired by shakespeare on this idea of neg.cap. ie.shakespeare always leaves his plays with mysteries and unswered questions in it. (eg. we never find out if lady macbeth is pregnant, and we never know the relationship that desdemona and othello before they get married)
hope this helps if you're still unsure just ask!