You may be using Matlab to create graphics. Some considerations:

1. Save all data or all scripts. Get in the habit of saving data as .mat files.
2. Create scripts that will load in .mat files and plot the data. This means if you ever need to regenerate pictures, you can do it very easily.
3. Similar to above, you may want to save .fig files of the pictures. Again, it allows fine-tuning. (In fact, you can extract raw data from .fig files via scripts if you look into it). To save such a file, simply click File > Save-As on the figure window.
4. Use export_fig package (Matlab file exchange) to export to pdf format. In general, output to PDF format unless the image is very detail-heavy (surface plots, contour plots, etc.). This ensures that the image is scalable and crisp.

Once you have downloaded the export_fig package, unzip it and move the folder into a unified functions folder on your computer. Refer to the startup.m guide. By doing so, you can issue a command like

export_fig 'test.pdf' 

in order to produce a PDF of the currently targetted figure.