Try to arrive in Vienna at least one day before the conference to adjust to the time zone (Central European Time.)

Try to sleep on the plane and drink plenty of water. Drinking alcohol while travelling worsens jet-lag.

On the day you arrive, do some light exercise like going for a walk (ideally in the sunlight.)

It can take many days to overcome jet lag so plan your conference schedule accordingly.

See also Dealing with Conference Exhaustion under Your Health.