I would say this question is kind of difficult not just because it varies from database to database and environment and environment but also from person to person and the particular goals that you set.
For example, depending whether you want to see a big picture of how data is organized within normalized or de-normalized tables or study what a particular t-sql stored proc or function does, or how a complex-looking view pulls data from many tables and other views, - you may want to see and ER diagram (ER = Entity Relationships). Of course if database is huge and has 500 or 2000 tables in it your ER diagram will be the size of a building and useless for your review :).  I usually do ER-Diagramming of a particular subject area that I am interested in that involves a dozen or less of core tables and views containing the data that I need to learn and understand. You can do such diagramming using a variety of tools, including the one built-into SQL Server (not really good and flexible...) or something more sophisticated like ERwin or MS Visio.

Database Documentation can be of paramount importance and use but it is usually a rare luxury in most IT shops.
       Using an example of AdventureWorks database that you mentioned,  here is what good documentation for it looks like (PDF file):  
      http://allstarsql.com/adventureworks2012.pdf

       It never hurts to ask your DBA for such documentation :). At least you can ask. One shop out of 100 will have such documentation, you may just get lucky... 😎

I also do this for analyzing stored procedures or complex views: finding dependencies. I.e., objects that the stored proc depends on (uses in its code) and/or objects that use the object that I am analyzing. Since the built-in Sp_depends is not really dependable for such purposes, a third party tool may be recommended such as Redgate Dependency Tracker.  

Some SQL Server undocumented stored procedures showing up and down level dependencies can be useful too:
     -- Value 1053183 shows objects that the specified object is dependent on
    EXEC sp_MSdependencies 'vw_MyComplexHeadacheView', null, 1053183

     -- Value 131527 shows objects that are dependent on the specified object
    EXEC sp_MSdependencies 'vw_MyComplexHeadacheView', null, 1315327