Many hobbyists do not realise that papers can have grain. Knowledge of what grain is all about can help prevent things from going wrong when using paper
Not all papers have a grain. For some papers ~ such as newsprint ~ the grain is very pronounced. Handmade papers have no grain . One wag once explained to me that 'Wood comes from trees ~ Trees and wood have grain ~ the paper grain depends on the way the paper has been made from the tree trunk'. That person was correct ~ apart from the absurd last bit. Yes - wood does have a grain. The wood is well chopped and mashed ~ shaken and stirred ~ as part of the paper-making process. Some paper-making machines restore direction of the fibres.
I think it is worth explaining why I mentioned 'things going wrong' in more detail. The reason for that is my own history of bodging some projects by not knowing the importance of going with the grain. Learning by experience is an excellent method ~ but it can be painful. Bookbinding troubles sometimes manifest themselves right at the end of the job. There is no remedy....start again....ouch!
Hopefully readers not have any troubles. Remember this ~ wet grainy paper swells more in one direction than the other. Once pasted it swells. Then, as the paste ~ and paper ~ dries, the paper tries to return to its normal size. It normally does this by causing wrinkles or curls ~ which can be very hard to get out. Such unwanted bending can spoil the finished product, putting hard work to waste. The cure is more careful attention to pasting ~ and patient drying under gentle pressure. Patient can mean a week or two. Pressure does not have to be too great if applied whilsst things are still damp. Once a job is dry and curled or warped it may be impossible to retrieve the situation.
I have done some pictorial demonstrating which is interesting to see ~ and would be most beneficial for students to try for theselves . There is also a picture of something that went wrong .
~ find the direction of grain of the paper ~ and adopt good practice
~ the grain always runs parallel with the spine or hinge ~ from head to foot. An A5 folio or booklet made from folded A4 paper will be cross grain ~ it works ~ but try to avoid it
~ paste your paper and let it swell to its full extent ~ a minute or two ~ re-paste any bits that dry out ~ do not work in bright sunshine in mid Summer
~ wherever possible paste both surfaces so that they both have a chance to swell ~ make sure both papers have the same grain direction
~ dry under sufficient pressure to prevent curl ~ change your chip paper frequently (say 20 times) over the next week or more 
~ to hasten drying do not use any heat. At any one time a busy bookbinder will be working on a score of books. Most of them will be sitting in a press ~ slowly drying ~ without warping
A related issue is the pattern of printed decorative papers. There is more to say about that topic. Suffice to say ~ for now ~ that usually the pattern and the grain match-up.
More about this is available under several headings ~ it is an important topic ~
~ Why grain is important ~ .
~ Papers with grain, or no grain at all ~ .
~ Ways of finding the direction of paper's grain (1) tear it ~ .
~ Ways of finding the direction of paper's grain (2) wet it ~ .
~ Ways of finding the direction of paper's grain (3) ~ cheat it .
~ Ways of finding the direction of paper's grain (4) ~ paste it ~ and regret it .
~ Ways of not finding the direction of paper's grain (5) ~ guess it