Flora and fauna
In March/April (best time to go there) its generally very hot and humid. But the scenic beauty and landscape will soothe it. Do wear sunscreen and sunglasses. Also wear a cap. You can carry an umbrella while you walk.
You can also pay the local fishermen to take you on day trips to mangrove creeks (Bridget Creek is nice) or places like Mt Harriet National Park (where you can beach your boat and go birdwatching). Don't pay more than Rs 2000/day for the boat, and you can often bargain it down to much less. Be sure to check with the Forest Dept before heading out, as many destinations require certain permissions.
Also there is package tour available for Ross Island, North Bay and Viper Island at Rs 360 per head. The trip starts at 9 am and ends at 5pm. Complimentary lunch and breakfast is provided by the tour operator.