What is Unwise Consideration? I am reading a book on the jhanas and it stated, 


  All hindrances arise from unwise consideration. To overcome them one must apply wise consideration.


Now i think what unwise and wise consideration is the things you focus on. Unwise Consideration maybe focusing on your past or your future asking question that have no really meaning pondering them. While wise is focusing on suffering and overcoming it. Is thia correct?
In short:


having Vipallasa (see: Vipallasa Sutta), 


I.e., not seeing the three marks of existence

having the unwholesome roots


having craving and clinging due to the unwholesome roots arising
having defilements

having the 5 mental hindrances
having ignorance


not aware of causality (4 Noble Truths, Dependent Origination, Conditional Relations) due to ignorance (not knowing the 4 Noble Truths, Dependent Origination, Conditional Relations)
because ignorance also displaces the rights view no knowledge of the right view (not knowing or wrong understanding items mentioned in Samma Ditthi Sutta) or having know the wrong view. 



Piya Tan has done a good detail explanation which I have quoted below:


  Ayoniso manasikāra, as such, means “not directing the attention to the roots of things” or “directing
  the attention away from the roots of things,” that is, not observing phenomena as they truly are, not noticing
  that they are impermanent, unsatisfactory and not-self. As a result, wrong view arises, and when this
  become a habit, wrong view is reinforced so that it remains as a latent tendency (anusaya). Let us examine
  a little more as to how this happens.
  
  “Unwise attention,” according to the Vibhaṅga, is the regarding of what is impermanent as being
  permanent, what is painful as being pleasurable, what is not self as self, what is foul as beautiful. 6 The
  Majjhima Commentary says these are the four “perversions” (vipallāsa). It explains unwise attention
  (ayoniso manasikāra) as attention that is unskillful in means (anupāya,manasikāra), attention shown the
  wrong way (uppatha,manasikāra), that is, by way of the four perversions, namely:
  
  what is impermanent is taken to be permanent (anicce niccan ti);
  
  what is painful is taken to be pleasurable (dukkhe sukhan ti);
  
  what is not self is taken to be self (anattāni attan ti); and
  
  what is impure is taken to be pure (asubhe subhan ti).
  
  The (Akusala,mūla) Añña,titthiya Sutta (A 3.68) says that the three unwholesome roots (akusala
  mūla) of lust, hate and delusion arise through unwise attention. Lust arises and grows through unwisely
  attending to a “beautiful sign,” that is, being captivated by what we perceive as attractive in a thing. Hate
  arises and grows through unwisely attending to a “repulsive sign,” that is, what we take to be unattractive.
  And delusion arises and grows through unwise attention itself. In other words, delusion is present when
  there is lust or hate. Delusion arises and grows because of the four perversions mentioned above.
  
  On a deeper mental level, as explained in the (Āhāra) Kāya Sutta (S 46.2), unwise attention gives
  rise to the five mental hindrances—sensual desire, ill will, sloth and torpor, restlessness and remorse, and
  doubt—which prevent us from attaining samadhi, that is, meditative mental focus, or any kind of wholesome
  attention.
  In short, we are hindered from our mental development.
  
  Unwise attention, in other words, is based on ignorance, which starts off the dependent arising of
  mental formations (saṅkhāra), which are karmic activities, and these lead on to a whole mass of suffering,10
  and the prolonging of the samsaric cycle (vaṭṭa) (MA 1:64 f). In short, unwise attention is the root
  of samsaric existence. Unwise attention is food for a lack of mindfulness and full awareness, which in
  turn increase ignorance and craving.


Introduction to Yoniso Manasikāra Sampadā Sutta by Piya Tan. The next section discusses what is wise attention.

Also see my other explanation in these answers.