The most popular starting point is the Glenmore Visitor Centre, as there is a café and toilets on site. But if you can't get parked there, there's no need to panic as there's plenty more parking a little further along the road at Allt Mor and Hayfield car parks.
We parked along at Allt Mor recently and started our walk from here for a change. There is a very well maintained path right from the start that is suitable for walkers, buggies and bikes. You can follow the purple way markers for a circular route back to the car park, but we chose to join the main route to the Green Lochan for a slightly longer walk.
The Scottish Forestry Commission has some great map guides for these simple routes near Aviemore and the Green Lochan route can be found here. There are several paths int he Glenmore area to explore.