Best Time : Any time of the year, depending on the location you choose for trekking.
Tips : Hire a qualified guide to lead your trek; it's mandatory for foreigners while trekking, and highly advisable for Indians.
Trekking

Trekking is best way to pass your idle time. India has a good opportunities for the trekkers. The varied topography of India has some very special and unique things to offers you, at every step you put forward. The topography of India has unique species of biological species for you to explore and understand.
Be it north or south, east or west, India has a series of breathtaking trekking trails. Head for the Himalayas- for arid but gorgeously beautiful Ladakh and Zanskar, if you're looking for adventure; or make tracks through Himachal Pradesh- Lahaul, Kangra, Spiti, Kinnaur, and the Sangla Valley- for easier treks which take you through stunning landscapes and quaint villages where time stands still. Go trekking through Garhwal and Kumaon, the Satpuras near Pachmarhi, or go to the Nilgiris. If that is not enough, then there are plenty of other treks to try and enjoy. The Sahyadris in Maharashtra; the hills around Shillong, Kalimpong, and Gangtok; the Valley of Flowers and much more.
Some Exciting Trekking Routes
There's actually no end to the paths you can find, the trails you can follow, But there are some which are exquisitely beautiful :
Ladakh
Try trekking in Ladakh in the month of June to October. Trekking through Ladakh isn't easy- its' harsh, rugged terrain and inhospitable climate is enough to overwork the most seasoned of hikers- but once you've walked these trekking trails, you could easily get hooked for life. Some trekking routes in Ladakh are in the
Zanskar Region - The Best Treks
Spituk-Rumbak-Yurutse-Ganda La-Skiu-Markha-Nimaling-Kongmaru La-Chogdo-Hemis-Leh.
Lamayuru-Wanla-Hinju Valley-Konze La-Sumdo Choon-Stapski La-Alchi.
Lamayuru-Prinkiti La-Wanla-Hinju-Konze-Sumdo Choon-Dung Dung La-Chilling.
In all these treks you will come across numerous beautiful sights and surroundings. You will find some Buddhist Monasteries and Gompas here.
Lahaul - Eco Treks in Himachal
Nestled in the far northern corner of Himachal Pradesh, the valley of Lahaul lies in what would surely rate as some of the most beautiful alpine territory in the Indian sub-continent. The valley is divided by the Chandra River, and lies along the periphery between the states of Himachal Pradesh and Jammu and Kashmir. To its south are the apple orchards and green pastures of the Kullu Valley; to the north is the vast alpine desert of Ladakh. Bounded by these two extremes of terrain and plantation lies the Lahaul Valley- with its glaciers, its barren mountains and the idyllic Chandratal Lake. A region of harsh terrain, friendly people and mountains which make for some memorable treks.
The Nilgiris - Trekking in Western Ghats
The junction of the Western Ghats and the Eastern Ghats, the Nilgiris - the `Blue Mountains'- are amongst oldest mountain ranges of India. The hills, a part of the Nilgiri District of Tamilnadu, stretch across the borders of the state into the adjoining states of Kerala and Karnataka. Easier to trek than the mighty Himalayas, the Nilgiris are often seen as being better suited for amateur trekkers. The gentle slopes and moderate climate of the region mean that even those with little or no experience won't end up getting completely fatigued. The beauty of the Nilgiris, however, is such that even veteran hikers will enjoy themselves.
The three main towns of the Nilgiris- Ooty, Kotagiri and Coonoor- are perfect bases for interesting treks into the Nilgiris. A trek through the Nilgiris is a fantastic way to see the hills - to explore the forests of rhododendron in full bloom; to visit the wildlife-rich sanctuaries of Mudumalai and Mukurthi; to walk through rolling green lowlands and along rippling streams. Trekking here is an absolute pleasure.
Sangla Valley - Trekking Routes in Himachal

The Sangla Valley is a gorgeous swathe of green, dwarfed by the surrounding mountains. The clear waters of the Baspa run between orchards of apple and apricot, through villages; an area so lovely that the inhabitants actually say that this is the place where the Gods live.
Spiti
Spiti is a sub-division of the district of Lahaul-Spiti is in fact, much like Ladakh - treeless, harsh, bitterly cold. Peopled here are remarkably friendly, warm and hospitable. The little vegetation there is, stretches along the rivers and in places where, because of irrigation, the people have been able to plant crops and trees.
Though Spiti is still an undeveloped area - with few facilities outside the main town, Kaza, not many trekkers complain about it. Walk along the Spiti river; trekking up to one of the thirty-odd Buddhist monasteries or trek to one of the villages which cling to the mountainsides. Wherever you go, Spiti is undeniably beautiful, whether you're looking for panoramic views, quiet old monasteries, or friendly villages.
NOTE :
Ecology is extremely delicate, so be very careful not to disturb it while trekking through the areas. Be especially cautious about disposing of waste; carry out all tins, bottles, altogether don't leave rubbish behind you.
Things to Carry
Carry heavy-duty shoes, a rucksack, Heavy equipment- such as tents and sleeping bags, basic cooking equipment and food. Heavy woollens, waterproof jackets and spare clothing must be packed as well, good sunscreen and sun glasses.