How should I describe a result from a submitted paper such that the reviewers can do their work? A month ago, I submitted a paper to a prestigious journal. In that paper, we proposed a general method (method A), and we proposed a set of methods  for doing some work based on this method A. I now have to work on another paper, which relies on method A, which I will be submitting to a less prestigious journal. Since I need this paper to graduate (I am a PhD student), I can't wait for the first one to be accepted before submitting the second one.

I didn't find any policy regarding referencing a submitted paper in the second journal (from Elsevier). 

Is it a good idea to very briefly describe the method A in the second journal paper and also reference it as a submitted paper? Method A has some proofs which I will not restate in the second paper. 

This way, the reviewers will be able to do their work. Note that it is very important that I don't want to hurt the chance of acceptance of the first paper or my reputation in any way. 

In other words, how can I describe a result from a submitted paper so  that the reviewers can do their work?

What would you suggest for someone like me who has to submit another paper (for faster graduation) in this situation?
When submitting a paper, you are normally able to provide attachments for consideration by the reviewers. You can include a draft of the submitted manuscript as a reference for the readers.

However, if you're in mathematics or another field which encourages preprints, you should in principle be able to post the paper on a repository like arXiv and point the reviewers to the repository version while the paper is under consideration. If the paper is accepted and appears in print before the new paper is accepted, you can change the reference in the proof stage.

What you can get away with depends upon the editorial policies of the journal. Some journals require you to provide copies of any material that is unpublished (such as correspondences with other researchers or unpublished manuscripts). Other journals will let you get away with less. But in general, you need to show some sort of evidence that the work is under consideration. Perhaps an email confirmaing submission, plus the abstract, will suffice?