So, in general the recommended weight for a weighted blanket is 10%+1 lb for someone. The maximum weight is 20% of their weight. So you would want somewhere between 5.4 lbs and 8.8 lbs. One of the reasons people do the going up to 20% of the weight is for growing children, while others do that for people who like lots of squishiness. I'd recommend somewhere in that range, but not going above it.

The basic idea for it, is that you want to make 4"x4" squares in the blanket, and fill them equally with the poly pellets. So, split up them into the amounts you'd need for the squares for 4"x4" squares for the top of a twin bed, sew a row of squares, fill a row of squares, repeat until its filled!

In detail what I did to make mine is here: http://turtleisaverb.blogspot.com/2014/0...nkets.html