I have detailed a process I follow for updates:

http://www.glass.lu/Blog/SitecoreUpgrades

I normally try to split DB upgrading from code upgrading.

This allows me to run the DB upgrade process of vanilla Sitecore instances where any customisations won't interfere with the db upgrade process.

I then upgrade the code as per the SC upgrade guides (and yes this means going through each one). This can take some time because the config changes a lot, my last upgrade from 8.0 to 8.1 u3 had something like 150 pages on config changes to review.

Once I have upgraded and tested my DB and code locally it is then very easy to roll this out because I only need to perform the DB upgrade in each environment which again is done with vanilla Sitecore instances.

More information on the process can be found here:

http://www.glass.lu/Blog/SitecoreUpgrades