For a first Bangalore visit, the biggest mistake is trying to cover too much in one day. Bangalore is spread out, and traffic can take a large part of your sightseeing time. It is better to group places by area and leave some free time between stops.
Choose your stay based on the areas you plan to visit. Staying closer to your main activities can make the trip much easier. Also, check your travel route before leaving, especially during busy hours.
Do not plan every meal or activity in advance. Leave some room to try local food, explore a market, or spend time in a nearby park or cultural place. Weather can also change, so carrying a light layer or rain protection can be useful.
Most importantly, keep your first trip simple. Pick a few places that match your interests and enjoy them at a relaxed pace instead of collecting as many attractions as possible.