5% skimmed milk powder in TBST, it should work for most western blot, but you can try to adjust and optimize the concentration based on the result you got.

Skim milk is available in the shops in a very cheap price. You can use that milk if it used safely in your work.

You can purchase blocking-grade skim milk powder from a scientific company, such as 'Nonfat-Dried Milk bovine' from Sigma (see below link), and use it to prepare 5% blocking buffer in the solution you need..

( http://www.sigmaaldrich.com/catalog/product/sigma/m7409?lang=en®ion=US )

Thanks all i appreciate your suggestions 

Hi Zaynab,

From this article, Block, Stock and Barrel – A Guide to Choosing Your Blocking Buffer [ http://bitesizebio.com/21454/block-stock-and-barrel-a-guide-to-choosing-your-blocking-buffer/ ], before you use skim milk as a blocking agent, you should know the warning mentioned below:

"The cheapest and most readily available blocking option is skim milk powder. Skim milk powder can either be purchased from a scientific company or over-the-counter at a supermarket. Typically milk powder is used in a 2.5-5% solution. But be forewarned, milk contains a mixture of proteins including phosphoproteins, for this reason milk should not be used if you are using phospho-specific antibodies. That is, unless you want extra background noise, which of course you don’t."

Thanks alot Salamma and Yuan it helpful  

the easiest method as mentioned by colleges is to buy it directly from supermarket or a company

 but if you want to prepare fresh skimmed milk i.e. liquid

pasteurize and then separate  using Centrifugal  force   to the extend of required skimming

If you decide to buy skim milk from grocery store, you should buy the 'powder' milk, not the liquid one. It will be easy for you to calculate and make needed concentration. For example, you want to prepare 5% blocking solution, you just measure 5g of the milk powder and dissolve in 100 mL of whatever solution you need.

There are two way : first buy skim milk from store , you should by the powder milk . the second you can made that by first take whole milk with fat and you pastured it at 65C for 30 minutes, after that you should lift it to removed the fat layer and fater that you can get the liquid skim milk  ( the solid phase is around 11% ).