There are a number of tools available for tuning plugins and configurations. These tools can identify which parts of a process or config section require your attention.
Rules Debug Log
The Rules Debug Log is built into Rules and is available through the settings page. It's a useful complement for the configuration and programming of processes because it follows what rules are executed and displays that information in the help region.
For example, it can show what conditions are evaluated TRUE or FALSE, which variables were used, what order operations were executed, how long time each step takes, and more.
Viewing the Rules Debug Log output is a helpful way of pinpointing why something unexpected is happening. Clicking the  link next to an event will take you to the Rules UI where you can fix the miss-configured rule.
You might want to set "Show debug information" to "Always" while you're working on a rules, and "In case of errors" while you're making other changes on your site.
Devel Rules (sandbox) adds a helpful section in Rules for builders, developers, and inquisitive admins. This module can print a summary of all available Data types, Entity properties, Actions, Conditions, Events, and Components. This summary includes the name of the module providing it, the label, base function, and most importantly, the data types it provides and expects. This can be useful when determining the reasons why certain values are available in the data selector and why others aren't.
If variables are not behaving as you expect, you will find the Rules action Debug value useful (provided by the Devel module). It prints out a krumo dump of a variable that you choose, making it available for inspection. Potential improvements for this are in https://drupal.org/node/1085234