Building on the answer above....

Once you migrate to Gmail, you can setup a forwarder in Yahoo mail to handle any future email.  http://answers.yahoo.com/question/index?qid=20131017133634AA9FNVW

I'd also setup an auto-reply in Yahoo letting people know you changed email addresses.

 http://help.yahoo.com/kb/index?page=content&y=PROD_YSB_BZMAIL&locale=en_US&id=SLN17479&actp=lorax&pir=7HthGQlibUlfPalRk9tbOEXwzlWdqV6ynVEdNQ--

Then you can eventually remove the forwarder and close out your old Yahoo account (or keep it open and occasionally check it manually). That way, you receive less "junk" to filter through.

Building on Chris Thompson’s answer…

Once you migrate to Gmail, you can setup a forwarder in Yahoo mail to handle any future email. (See this resource for details.)

I'd also setup an auto-reply in Yahoo letting people know you changed email addresses. (See this help page for details.)

Then you can eventually remove the forwarder and close out your old Yahoo account (or keep it open and occasionally check it manually). That way, you receive less "junk" to filter through.