You need to supply more details than you have in order to get to the core of the issue.
What version of Premiere Elements are you using and on what computer operating system is it running? What do your computer resources look like, installed and available RAM, total and free hard drive space, location and free space for the Scratch Disks?
What are the properties of the source media that you are putting on the Timeline?
Based on the properties of your source media, what is the project preset that you or the program are setting in the new project dialog?
Video (video audio compression, frame size, frame rate, interlaced or progressive, file extension, duration, PAL vs NTSC, camera source, etc.)
Photos (how many, what format, what pixel dimensions)
What is your export choice and settings?
Let us start here and then we can decide the troubleshooting strategy.
Rendering does not alter the exported file quality in any way. Rendering is ONLY for use during editing. The rendered video is not used at all when you do a Publish/Share. What render does is to create a single video of the contents of your timeline, thus allows for easy playback during editing. That file thus generated can be configured for a high or low quality (Edit -> Preferences -> General tab, last option "Timeline render quality...")
What matters during export is what ATR mentions,
1. the source file
2. the project settings
3. the export presets
So if you want a higher quality output, we need answers to what has been requested.