The best months for trekking are February till May, and October and November. During these months the temperature during the day is nice and it is not too cold in the night. After Monsoon season, in October and November the sky is clear so you can see the Himalayas extra nicely. During Monsoon, in June, July and August the trails are slippery and the mountains are barely visible. From October till March it is dry and sunny, but during the nights can be cold. So make sure to take warm clothes.