Guidebook with maps/step-by-step :
Start hiking by climbing up the path heading up along the Py waterfall. At the top of the waterfall, the trail keeps running along the stream.

After 2 hours hiking, you get up to the Plaisance refuge (alt. 2160 m). The path goes up quietly towards the Plan Séry pass.
Keep walking along the marked trail after the Plan Séry until you get to a junction (alt. 2320 m) and take a path on the right heading to the Palet pass which overlooks Lake La Plagne. You reach the GR5 once you get to Grassaz.

Walk along for 350 m then turn towards the Grassaz pass. You walk not far from Lake Verdet and see Lake Grattaleu.
Once you get to the pass, you can begin walking down by heading to the hamlet "Laisonnay". On this trail, you'll see the Park rangers' chalet, the alpine chalet of Plan du Sel and the Glière refuge.
Tips :
Families or people who don't want to do the whole tour can go hiking 2 or 3 days. Don't forget to book in advance your night(s) in refuge(s).