Start with the boring but important part: make sure routine vaccinations are current, meaning tetanus-diphtheria, measles-mumps-rubella, polio, and the usual childhood schedule, because these diseases still circulate in parts of the world where local immunity gaps exist. Travel clinics see more trouble from lapsed routine vaccines than from exotic ones.
On top of that, the commonly recommended travel vaccines depend on destination, trip length, and what you'll be doing. Hepatitis A and typhoid are the workhorses for regions where food and water hygiene is variable. Hepatitis B matters for longer stays and any possibility of medical or dental treatment. Rabies pre-exposure vaccination is advised for rural travel, long stays, cycling, or anywhere prompt treatment would be hard to reach. Japanese encephalitis, meningococcal, cholera, and yellow fever are region- and activity-specific, and yellow fever can be an entry requirement, not just advice.