What steps do you take to ensure that the final video renders at the highest possible quality while remaining within file size and format constraints for its platform?

These days Software's come up with Presets for Each platform that already have the highest possible settings recommended by the platform. The only platform that I personally have to manually adjust for is Instagram and I have found a workaround for their platform that retains the best quality when it actually gets there with the least amount of compression.

Render your footage at Max depth and Render quality set the Bitrate to 25mpbs and use Vbr Pass 2. 

Then take that footage into Handbrake its a free Open source software . 

Use these settings. 

In the  Summary Section Web Optimized Check

In the Dimensions Setting set Resolution Limit to none.

In the Video section choose The Frame rate to same as source make sure in the Premiere setting when encoding for Instagram its already 30 fps otherwise change that to 30fps in handbrake.

Choose Constant frame rate

Constant quality to 21 or 20.

Thats all you need the file size will be super small and it will not lose quality.

Selecting bit rate is the most important one to control the file size. What I do most of the time is to check the bit rate of raw footage and manage to select the same for the final product. 

Also selecting bit rate should be according to the platform requirement, like most of the time for youtube I select 10,000 kbps even though the raw footage bit rate is higher.  

It requires steps that balance quality, compression, and technical requirements.
Here's a breakdown of those steps:

1. Platform Requirements
Each platform (YouTube, Instagram, TikTok, etc.) has specific file size, format, resolution, and bitrate recommendations.
Maximum file size allowed, supported file formats, resolution and aspect ratio, duration limit, frame rate limit

2. Choose an Appropriate Codec
Use formats like MP4 (H.264 or H.265) to ensure compatibility with most platforms while keeping file sizes relatively small.

3. Proper Bitrate
Platforms typically provide bitrate recommendations (YouTube recommends 8-12 Mbps for 1080p 60FPS).
Bitrate control is key to balancing file size and quality - higher for fast motion, lower for static shots.

Be careful balancing these factors—resolution, bitrate, codec, compression methods, and platform requirements—you can ensure that the final video has the best quality possible within file size required!