Can I Compress a huge table on SQL?
Since you're using SQL Server 2012 Standard, you're not able to take advantage of DATA COMPRESSION.  It's an Enterprise feature up until SQL Server 2016 SP1.  When you're able to upgrade, you should check out that functionality.  'In addition to saving space, data compression can help improve performance of I/O intensive workloads because the data is stored in fewer pages and queries need to read fewer pages from disk.'

However, there are a few things you can do now to possibly reduce the size of your databases.  Look for the tables that are taking up the most space and...


Archive (and delete) any data that doesn't have to reside in the database.  Afterwards, rebuild indexes on any affected tables so you can consolidate the data into fewer pages.
If you haven't done so already, consider increasing the fill factor on your indexes to 100%.  Having your pages as full as possible can reduce the overall space needed requiring fewer pages in memory.  Afterwards, rebuild indexes on any affected tables so you can consolidate the data into fewer pages.  Check out Does index fill factor affect fragmentation?
Try to find unused or redundant indexes.  If an index is not being used, it's just taking up space in the database for no reason.  Likewise, you may be able to consolidate several redundant indexes into fewer ones.  There are numerous free tools and queries available by searching for 'sql server unused indexes'.  A personal favorite of mine is sp_BlitzIndex.