The question that many people struggle with when developing their own interface for the first time. What separates the good interfaces from the bad interfaces?
In my opinion, there are five basic characteristics which make an effective interface
3.Ease of Use
The most basic characteristic of a good interface is keeping the layout clean. Most interfaces are divided into seven main parts. The Action bars, the minimap, the Unit Frames, Chat box/Combat log (these can sometimes be two different things.), party frames, buffs/debuffs (again can be two separate areas), and Cast bars. The addons I link to are my personal prefference for cleanliness in those categories, if you have an addon you prefer by all means enjoy it.
Action bars: A crucial part of any interface. The action bars can be minimalistic showing only that which is most vital or they can be all inclusive providing a button for every situation. It is really up to you. A common practice is to either lower the opacity of well known keybound action bars or to completely hide them. For action bars I recommend the addon bartender4, it can be found here. There are many choices for a clean set of action bars. Do you choose the block in the bottom full of everything and anything, do you thin it out and put only the necessary? Do you use long bars covering most of the bottom of the screen? I haave found that for most casters the choice of a block is the best wayt og o simply because of the sheer number of spells and abilities they have.
Minimap: the minimap can be many different shapes and sizes. The most common and in my opinion the cleanest choice is the basic square shape of the minimap. I prefer the addon Pminimap to provide a clean and simple minimap for my interface. It can be found here.
Unit Frames: The unit frames are in the simplest terms, the indicator of health/mana/rage/energy of your character, your target, target's target, and pet. The most common addons used for unit frames is Pitbull, Xperl, ag_unit frames, the default unit frames provided by blizzard, and many others. Blizzard's provided unit frames are good at showing pretty much everything you need to know, however they are not the most effective choice. My personal choice for unit frames is pitbull because of it's customization options. Many people like the choice of Xperl because of it's ease to set-up in comparison to Pitbull. Where do you put your unit frames? the top like blizzards? The bottom middle of your screen for quicker viewing in times of stress? I prefer the bottom middle for PVP purposes because it allows me to find health of my target and myself quicker when in tight situations.
Chat box/Combat log : My personal choice for chat box addons is Prat. It is simple and easy to configure Some people prefer the choice of WOW Instant Messanger to handle their whispers. There are also many choices for combat log choices. My choice for raids to keep it clean is the addon eavesdrop found here.
Party Frames: Party frames often come with unit frames addons like pitbull or Xperl, however if it doesn't I recommend using grid to show party frames and raid frames. Grid may take a little while to configure, in the past I made a post about a video I used to configure grid for my raid frames.
Buffs and Debuffs: Of course blizzard provides the buffs and debuffs for their default interface, however if you are moving around other elements of your UI you often would prefer your buffs and debuffs to be in a different location or size. To do this the two addons which I recommend are Satrina Buff Frames for anyone who wants to keep the look of the blizzard unit frames. Can be found here. For those who prefer the look of bars for their buffs I recommend elkano's buff bars which can be found here. I have found that for those who raid and gain a large amount of buffs that SBF is the better choice than EBB because of the amount of screen space taken up by the bars compared to the small buff squares.
Cast bar: Like most of the other elements of a UI blizzard provides their own cast bar, however just like many of the other elements blizzard's cast bar lacks a few important options that other addons can provide. My personal choice for cast bar addons is Quartz, it can be found here. Quartz provides a way to help counteract latency majority of the time.
I hope these basics to creating a clean interface help you to build a better interface that helps fit your needs. Expect the continuation to this subject in the near future.