There are a few options for streaming software out there. I currently use Open Broadcaster Software (OBS) so that is what we will be looking at in this tutorial. I also only stream on Mixer so my settings will be tailored for Mixer's zero latency FTL setup. Some of these initial steps will only need to be done one time, unless you purposely go back to fine tune some of these adjustments, which is recommended once you are comfortable with the options and are ready for trial and error. But in the meantime, lets get you setup and I'll show you some of my setup options.
Step 1: Download and install the latest version of OBS
Step 2: Setup Stream Settings and Adjust Output Quality Again most of these settings will only need to be entered once as they are saved and used each time you broadcast. They will however always be available for adjustments down the road as you experiment what works best for your internet connection as well as your viewers. Open OBS, then the first thing you'll want to do is head to the stream settings which can be found under 'File -> Settings -> Stream' This tutorial will be based on Mixer's FTL (zero latency) technology so hopefully your internet connection is capable of handling this. Change the 'Service' to 'Mixer.com - FTL' via the pull down menu.
The Stream Key is your unique identifier which connects your OBS software to your Mixer account. This unique key is important and should not be shared. To get your key, head over to Mixer.com, login with your streaming account. Click your avatar in the top right corner -> Manage Channel -> 'Broadcast' tab -> Then click the copy icon and paste it into the Stream Key box in OBS. Apply your settings. 
Step 3: Adjusting Output Quality Now that your Stream tab is setup, your OBS should be able to talk to Mixer and allow you to go live. This section will go into some of the finer details regarding your overall stream quality. There is a fine balance that you will need to find between your CPU availability, internet bandwidth and any limitations of the hosting site and your viewers connections. It would be best then to work with a baseline setting and adjust from there. The following screenshots will outline settings that I typically use given my hardware and internet bandwidth. This gives me a good stream quality while hitting the CPU and internet upload speeds a bit harder than average. Head over to the Output tab in your OBS Settings. Switch the Output Mode to 'Advanced' to unlock some additional options. Encoder: x264 (software encoder), which would be your typical default encoder. Bitrate is most likely going to be the variable you will be adjusting as you tweak your stream output. Bitrate deals directly with your stream output quality and is dependent on your internet upload speed. I won't go into too much detail here as there is already plenty documented on the internet as far as 'best settings' goes. I would say to play within a range of 2500-3500. You should be able to get by with a lower bitrate setting on lower motion games vs. the higher bitrate requirements of faster moving games. So again play around with this, but for the purposes of this tutorial I will leave this at 3000 bitrate with a CBR Rate Control. The CPU Usage Preset is set to 'faster' which is one step slower than the default of 'veryfast'. For this setting, the faster this is set the less strain there is on your CPU resulting in a lower quality output. Therefore the slower this is set, more strain on the CPU resulting in a higher quality output. The Profile is set to main based on Mixer recommendation. I believe this setting has a direct impact when viewing on mobile devices as certain devices may not be able to display high profile. The Tune setting is set to zerolatency based on Mixer recommendations. From what I understand the Tune setting has a sight effect on the time required to output video, in milliseconds. x264 Option: 'bframes=0' based on Mixer recommendation.
For Nvidia graphics card owners - you will have to option to encode with NVENC H.264 Encoder: NVENC H.264 (hardware encoder which will minimize CPU usage) Bitrate is set to 3000 bitrate with a CBR Rate Control. Again you have to freedom to adjust this as you see fit The Preset is set to low-latency. Experiment with this setting and leave at Default if you have any issues. The Profile is set to main based on Mixer recommendation. I believe this setting has a direct impact when viewing on mobile devices as certain devices may not be able to display high profile.
Step 4: Creating Scenes Scenes are collections of elements that will be output to your channel. They are what your viewers will be seeing on stream as you activate them. I have multiple Scenes created for different game sources. I also have separate scenes for my Intro, BRB, Outro splash screens as well as my Raider Video. These are activated with a simple click of a button. Scenes can be dulplicated (by right clicking) then modified, if you want to create a similar scene. They can also be reordered to your liking.
Step 5: Creating Sources Scenes are composed of a collections of sources. These sources are then main components in building a scene. Some example sources are your game inputs, webcam, mic, screen overlays, etc. This collection of sources really make up the entirety of your scene. You can click the eye icon to quickly disable or enable a source. Right clicking on sources bring up a menu with multiple options. Two important choices are 'properties' and 'filters' we will most likely go into more detail on some of these in the future.