Very broad question but you could do worse than park in something like WAM shares and add every 6 months or so. You'll likely get steady franked income and some growth. If you use a retail broker the cost shouldn't be prohibitive. If it's a large amount consider a part-bond portfolio through fiig or similar, or a managed index fund which accepts regular contributions.
Shop around and ask providers what they offer, else go to a financial planner.
