Use minimal capitalization. A heading starts with a capital, but other words should not be capped up, unless they are proper nouns. If in doubt, choose lower case.
Exceptions include: our Sun, Earth (the planet), and our Solar System, but not universe, moon, earthquake, earth (the soil).
Use a capital letter when you are writing the names of people, languages, places, and words relating to them:
Only capitalize the name of a machine if it is the only one in the world:
The Large Hadron Collider (LHC) started today, but other hadron colliders have been working for years.
The proton synchrotron at Fermilab has broken down. The Super Proton Synchotron (SPS) at CERN is still working fine.
Note: Do not capitalize a word to "prepare it" for abbreviation. So:
The theory of quantum chromodynamics (QCD) was developed from work in the 1950s. An interesting aspect of QCD is that...
The theory of Quantum ChromoDynamics (QCD) was developed from work in the 1950s. An interesting aspect of QCD is that...