The 20th edition of The BlueBook was just published in late June 2015, so some aids you find may not be up-to-date:
LexisAdvance has a CALI-like system to assist you in learning how to cite correctly. Go to Lexis Advance. Click on Research tab and drop down to LexisNexis Interactive Citation Workstation.
The following too can assist you in your source and cite-checking:
This guide highlights only particular publications on Lexis (both Lexis Advance and Lexis.com), Westlaw and Bloomberg Law. Always be sure to check each of them to see if the source cited is there.
You can also search them to find how other authors have cited your source in secondary sources or in cases or statutes.