By adding a if loop.first statement, followed by the Event Merge Tags you don't to appear for every ticket.
Example:
{% for ticket in TRANSACTION.TICKETS %}
{% if loop.first %}
{{ ticket.EVENT.VENUE_NAME }}
{{ ticket.EVENT.VENUE_ADDRESS }}
{%endif %}{% endfor %}
This ensures that Venue Name and Address only appears once/for the first ticket.
You'd then need to remove {{ ticket.EVENT.VENUE_NAME }} and {{ ticket.EVENT.VENUE_ADDRESS }} from the Event information in your template.