A different kind of blog post for different kind of trek event :)
Simple online search like "Trekking places around Bengaluru" will give plenty of places to go trekking. The popular places are usually crowded though and inevitably riddled with garbage. Apart from being good responsible trekker by not littering, try to help in cleaning garbage you see on path if possible.
So, while searching, go beyond first page results. See if you can get some blogger describing experiences of a obscure place. Or just take that extra step to scale a hill you saw someday somewhere while traveling. If it is easily accessible via public transport (by bus or train), the better.
As I put it before, spots accessible by public transport is better suited, especially when you are a group of more than 5 trekkers.
With lot more info available online, like etrain.info for passenger train details, it is easy to plan ahead. Take a note that trains on Sunday are lesser compared to other days in the week. Hence, jam packed on Sundays. Go lot earlier to purchase tickets, perhaps ask that one fellow who likes to reach lot earlier than scheduled time to book tickets for all. After all it is a team work and everyone can contribute in their own way :)
For early starts, might be difficult to get up, have breakfast and reach station in time. Easy to get decent food on major stations, but not so at small stations. So, again co-ordinate to see if some can get parcel for others.
Fruits (bananas, especially red ones, dates, oranges, apples, guava, etc) are handy. Home food would be awesome :P Get theplas or khakras if available in a shop nearby to your place.
2 or 3 liters of water is must for everybody to carry. Carrying tetra pack fruit juices is a plus. Or get Electral and mix with water when needed. Unlike western ghats, hills around Bengaluru mostly don't have water source on trail paths.
Trail and Terrain
Locals are usually helpful - be it info about trail, travel options, food, etc. It helps to have someone knowing the local language as well.
Attire according to place is important. It is reasonably safe to assume thorny bushes in hillocks around Bengaluru. Jeans and Corduroys are better suited than thin track suits which can get easily torn and draw blood in the process. Use breathable tops (preferably full sleeves).
If climbing a reasonably unknown hill, most likely there won't be a marked trail. If you find a good one, consider marking the path by scratching against boulders.
Caves are to be expected in hillocks. Often you'll have to backtrack. Often you'll have to attempt a little more to go further. Be reasonable and enjoy the journey, not necessary to reach the peak.
Flora and Fauna
Keen eyes could spot little beauties for macro shots. Be it flowers or bugs, sure to be found.