How to enter the second Jhana? I know you must abandoned applied &amp; sustain thought. Getting rid of applied is easy it's gone once the first Jhana is established. But how to you get rid of sustain thought? I have ready many books &amp; articles but i don't understand them to well. They say once you reach the 1st Jhana review them and see how gross the first really is. But wouldn't that break concentration &amp; push me back to square one?
From The Questions of King Milinda (translation mine):


  ‘Venerable Nagasena, what is the characteristic mark of vicāra?’
  
  ‘The characteristic mark of vicāra is pondering/mulling over (anumajjana), Your Majesty.’
  
  ‘Give me an example.’
  
  ‘For example, Your Majesty, if you strike on a copper vessel, it then rings for a while, it responds with a sound. Here, Your Majesty, the strike is a simile for vitakka and the reverberation is a simile for vicāra.’


So the "sustain" will cease all by itself when you stop "striking", there is no need to do anything separate.

As for your question about "review and see how gross the first jhana really is", this idea of "review and see as gross" comes from an entirely different context that was designed to explain Jhanas as steps of gradual removal of (initially coarse and then progressively finer instances of) Craving/Kleshas/Asavas towards cessation of dukkha and achieving perfect suchness. The first two Jhanas in this sequence can be further illustrated with a following allegory:

Let's say there once was a boy, who heard about this Luna Park coming to town that was rumored to have the best rides and the tastiest ice-cream. Everyone in town was talking about it, buying the tickets, and getting ready to enjoy. Just like the other people, the boy really wanted to go to that Luna Park and try the rides for himself. However, it happened so that he could not obtain the ticket and ended up staying alone in an almost empty town.

At first he was upset at his apparently bad luck, but then he said to himself: look, I can imagine how it is like at that Luna Park. It must be extremely crowded, with people pushing each other, hot and sweaty. The lines to the rides are probably very long. There is a lot of noise and screaming children are everywhere. The rides are nothing special, just going up and down, and the ice-cream is not different from what I can buy here any day. I, on the other hand, get to enjoy this entire town all to myself. I can walk in the park. I can gaze at the statues. I can sit on the benches. I can even walk into a city hall and sit on the mayor's chair - because everyone's gone to the Luna Park. How much better it is to not be at the Luna Park! How happy am I to have this quiet and peace all to myself. Can any Luna Park in the world be better than this quiet and peace? No, that would be logically impossible. It's a mathematical impossibility that something could be better than this quiet and peace. A Luna Park can be exciting at best, with lots of ups and downs - but it can't ever feel as sublime as this quiet and peace. And since I understand this fact, I'm not just lucky, I'm also wise. I understand what other people do not understand, and I can enjoy at a whole other level than they can.

-- As he thought so to himself, the boy immediately felt relieved, and the more he replayed these thoughts while going around the empty town, the more joyful he felt. Whenever he felt the joy was subsiding, he would look around and think up another reason for being glad. "Look!" he would say - "people at Luna Park are waiting in line to go to a toilet, while I have all toilets in town available to myself". He would then keep walking around, smiling to himself at that thought.

Until at some point the very effort of convincing himself started to feel redundant. "Why am I even repeating these thoughts to myself?" -- thought the boy. "This empty town is clearly much more enjoyable than the Luna Park, it's just a fact. Why don't I stop convincing myself and enjoy this beautiful town in peace?" -- and he did just like he said, stopped convincing himself and enjoyed the town in quiet and peace.

In this allegory, the boy is a meditator. The Luna Park is an idea of success. Enjoying the empty town is the first jhana. Thinking up another reason for being glad is vitakka. Pondering and smiling to oneself about that reason is vicara. Letting go of the effort of convincing oneself and just enjoying the town in quiet and peace - is the second jhana.

As you can see, in the First Jhana vitakka-vicara plays the role of a "peg" used to "push out" the unskillful mindstates:


  Just as a skilled carpenter or his apprentice would use a small peg to knock out, drive out, and pull out a large one; in the same way [...] when he is attending to this other theme, apart from that one, connected with what is skillful, then those evil, unskillful thoughts [about "the Luna Park" and "one's bad luck" -AV] — imbued with desire, aversion, or delusion — are abandoned and subside. With their abandoning, he steadies his mind right within, settles it, unifies it, and concentrates it.
  (from MN 20, Vitakka-santhana sutta)


The resulting withdrawal from the unskillful mindstates gives birth to "rapture and pleasure", and this process is repeated until "the entire body" is "pervaded" with it:


  Just as if a skilled bathman or bathman's apprentice would pour bath powder into a brass basin and knead it together, sprinkling it again and again with water, so that his ball of bath powder — saturated, moisture-laden, permeated within and without — would nevertheless not drip; even so, the monk permeates, suffuses and fills this very body with the rapture and pleasure born of withdrawal [from the thoughts about "the Luna Park" and "one's bad luck" -AV]. There is nothing of his entire body unpervaded by rapture and pleasure born from withdrawal...
  (from AN 5.28)


...once the defilements of mind have been washed away with joy to a sufficient degree, vitakka-vicara itself is seen as unskillful/redundant and is eliminated in turn:


  Just as the thought would occur to a man walking quickly, 'Why am I walking so quickly? Why don't I slow down?' So he slows down.
  (from MN 20, Vitakka-santhana sutta)


the resulting state is called the Second Jhana:


  ...with the stilling of vitakka &amp; vicara, he enters and remains in the second jhana: rapture and pleasure born of composure, unification of awareness free from vitakka and vicara — internal assurance.
  (from AN 5.28)


and then the other jhanas:


  Then the thought occurs to him, 'Why am I walking? Why don't I stop?' So he stops. Then the thought occurs to him, 'Why am I standing? Why don't I sit down?' So he sits down. Then the  thought occurs to him, 'Why am I sitting? Why don't I lie down?' So he lies down. In this way, giving up the grosser posture, he takes up the more refined one.
  (from MN 20, Vitakka-santhana sutta)