I was just about to start playing my Pokemon Platinum game on My Boy! Free on my android, when I accidentally overwrote my save with the title screen. Is there any way of getting back my previous save?
In all likelihood, there is not a way to recover saved files that you have already manually overwritten. However, there is a way to check, in case there were backups etc..
If any backups exist, you would need to manually locate them on your device. Some helpful tips can be found at this question which says:
In "My Boy!," .sav files are actually hidden in the same folders as the roms themselves.
However, you will need to have the full version of My Boy! in order to actually load any save games, as mentioned here.