Good timing to start preparing. A semen analysis checks count, motility and shape, and a basic hormone panel such as
testosterone,
LH and
FSH is worth doing since your libido has been low, as that can sometimes point to a hormonal cause.
Next Steps
Eat a diet rich in vegetables, nuts and whole grains, stay physically active, keep a healthy weight, and avoid smoking, excess alcohol and prolonged heat to the groin area such as hot tubs. A supplement like zinc or folic acid can help if a test shows you're actually deficient, but isn't needed otherwise.
Health Tips
If the low desire continues once these basics are in place, please see a doctor in person. It's often stress or lifestyle related, but a hormone check will rule out anything that needs treatment.