Converter: Video Converters like Any Video Converter are good for converting the videos for mobile and have many options like video bit rate, frame rate etc. So, I should preferable select Any Video Converter for converting videos that can be downloaded Here
Formats Supported: Know what formats are supported by your phone, and select it from the list
Video Resolution: Know the maximum resolution upported by your phone by playing simultaneous videos of different resolutions once you’ve got it, it can be used for further converting videos. Usually 320×240, 480×320, 640×480 are the common resolutions.
Video Bitrate: This is the key thing in any video conversion if you have a high end phones set it to maximum but it will also affect the size of output format. And for low end devices due to low processor and RAM one has to try each of the bitrate. The increase in video bitrate simultaneously increases the Video Qaulity.
Now Add Video files and start converting.
Note:- Keep experimenting with the videos by starting low resolution and bitrate to high resolution and bitrate viceversa because each phone has the different video playback support and GPU.