I do it in small pieces, do it small and do what they would do to make their quality of life better. My ultimate joke is that I will buy my parents a nice cottage, but that probably won't happen.
When my parents needed new car, I gave them 3k as a gift for downpayment on their Lexus CT200. My dad loves that car, he goes fishing far and loves paying little for gas while riding in a well made car.
This year they needed a new roof, so I surprised them by giving my dad a birthday gift that covered the roof.
Next year we are paying them back with grand child
.