In fact your files/data is not deleted immediately after you press the delete button. It is simply removed from the directory so that you cannot see it but actually it remains on the hard disk until a new data is written on at the available space. This kind of deleted files/data can be recovered from recycle bin in windows and from Trash in Mac OS.
If you have shift-deleted the file, you will not get your data easily because it is removed from the recycle bin as well. However it is still not completely deleted from your hard disk. This kind of lost and deleted data can be recovered by using special software that knows how to look for deleted files.
Recovering Maximum possible data from Windows or Mac OS: things to remember
As mentioned above that the deleted data is simply shifted to a new location until a new data is ready to occupy that space, it is always better to avoid using that PC if you want to recover your lost data. Once you recover your lost data, you can start using your PC/Mac as usual.
The more free space you have on your hard disk, the better is your chance of recovering the lost data. It is a good strategy not to use more than 60-70% of your hard disk capacity so that you can recover you data just in case you lose them.
Do not defragment your files because it will relocate the current files to the emptied space and reduce the chances of recovery. Once the data is overwritten, you will never be able to recover your lost files.
Use good quality data recovery software to recover your lost data without losing them further. There is no point in using poor/cheap quality data recovery software and messing up with files that have been deleted. Read the reviews of some reputed data recovery tools and decide which one is most suitable for your data loss situation.
If you have lost photographs or other audio video files, you should go for photo recovery software and not generic software. It goes without saying that if your storage device is physically damaged, you must seek the services of experts in this field. If there is no physical damage then choosing the best data recovery product is a challenge.