Diploma

Continue to work on expanding your knowledge. Stay curious. Find pockets where there is a lack of knowledge that is adjacent to what you have and learn. An example of this is say you learned Pro/E-learn Solidworks. This is called horizontal learning.
The second is learn vertically. Take a subject that you do know, say Pro/E again, and learn surfacing, get deeper into the subject.
Keep reading scientific journals, tech magazines (such as Design Engineering, etc). Go to the library and pick up books there.
Build your engineering library. Get the Machinery's Handbook, Roarks Formulas for Stress and Strain, etc. These will help in the future.
Next build a solid resume, online profile, and network. These will help get the next job. Always consider what the next step in your career will be. Look at your geographic area. Where will your next job possibly be? Work to be employable at those positions. Consider that engineering is a typically project-based profession. Projects come and go. Typical employment is only less than 5 years. Be ready to branch into new things.
Finally go to seminars, classes, conferences, etc. This is available at the local community college, work, or through organizations such as ASME.
Finally consider getting your masters or an MBA. Typically these are expensive, with not a lot of opportunity for payback, but this will be dependent on your geographic area.
All the best !!