I have recently booked Mahindra XUV7XO AX7L DSL AT variant. Now I am feeling this as a major shift from my existing car which includes (Car brand, Body type, Fuel type, Transmission), so I wanted to have reassurance on all these aspects. What should be do's and don'ts for me and realistic expectations and with each of these changes?

Moving from a 2014 Maruti Dzire to the Mahindra XUV7XO AX7L diesel automatic is a significant upgrade in every sense, size, performance, technology, and overall feel. So it’s completely natural to feel a bit unsure at first. 

The biggest change you’ll notice immediately is the size. The XUV7XO is wider, taller and sits on a longer wheelbase, so judging the car’s edges and positioning it in tight spaces will take a few days of familiarisation. Parking and manoeuvring won’t feel as effortless as your Dzire initially, but once you adjust to the dimensions, the added size actually gives you a more planted and confident feel on the road.
The diesel engine will also feel very different. It produces strong torque, which means the car pulls easily from low speeds and gathers pace much more effortlessly than your older petrol sedan. You may find yourself reaching higher speeds sooner than expected. So take it easy with the accelerator in the beginning until your right foot recalibrates to the stronger performance. On the positive side, overtaking and highway cruising will feel far more relaxed and less stressful.
If this is your first automatic, there is one habit you must consciously develop: use only your right foot for both the accelerator and brake. Many first-time automatic drivers instinctively try to use their left foot as if pressing a clutch, and that can result in accidentally braking hard. The safest practice is to rest your left foot on the footrest and not use it at all. Within a week or so, you’ll realise how much more convenient and less tiring an automatic is in traffic.
As for the diesel aspect, there is nothing to worry about, but modern diesels come with a Diesel Particulate Filter, or DPF. In simple terms, it’s a filter in the exhaust that traps soot to keep emissions clean. Over time, this filter fills up and needs to be cleaned. It does this automatically when you drive steadily for a while, typically a continuous 20-30 minute drive at moderate or highway speeds. 

If the car is used only for short city trips all the time, the filter may not get the chance to clean itself properly. So it’s good practice to take the car out for a longer drive every couple of weeks. Also, stick to the scheduled maintenance and don’t ignore any warning lights related to the system.
Fuel efficiency in city conditions may not match your old Dzire simply because this is a larger, more powerful vehicle, and maintenance costs will be slightly higher than those of a small sedan. 

However, what you gain in comfort, safety, features and overall driving confidence is substantial. Give yourself a couple of weeks to adapt to the size and performance, follow sensible driving and service habits, and the XUV7XO should give you many years of satisfying and stress-free motoring.