Concerning PCB design, you have to know which standard you have to be compliant with. It's depending on the use of your product (will it be used in heavy industry, medical, automotive, aeronautic, .... ?)

This will definitively the first item to know. What are the standards used in India ? (European, American, Indian ???)
This will define for example the isolation distances, which kind of PCB to use (epoxy, paper, FR4, FR2, and so on).

Let's take some examples.

In heavy industrial application requiring reliability for 10 years, you will have to choose a PCB like FR4 because of the isolation, then you'll have to respect some minimum distances between wires according to the voltage used. For example between 2 wires with 230VAC, you should have 3 millimeters between two wires or two pads or a pad and a wire or a wire and mechanical item. For 380VAC, this is 4mm. You'll see that you have to put a ground wire all around the board, that there is a minimum section for wires according to current value, that electric cables have some defined colours, that signalisation (led or lamps) have a defined color according to if that's indicate the voltage presence, a danger, a warning or a normal operation, ...

Then, in standards you have class of use (according to the final use of the product). The class will define the operating voltage, operating temperatures, humidity, the IP index, vibrations, EMC levels, and so on...

Example : a power board in heavy industrial environment should have more constraints than private use. You'll probably have to prevent your board from condensation, dust, some corrosive gas and so on...

For car application, I've seen that some big constructors doesn't use coat on PCB. For Trucks applications, it's nearly obligatory. This is due to the mission profile (a car has a life time of about 5 years and 200 000 kilometers. A truck this is 15 years and 1 500 000 kilometers and a truck can go in corrosive atmosphere (refinery). A military tank this is 30 years and 1000 kilometers)

Other example : in a car, according to if you put an electronic unit in motor area or in cockpit area, the operating temperature is -40°C to 125°C or 0°C-85°C. It will define the components you'll use. it will define also the housing you'll design.

Next for certification, your product has to be tested by an independant organism if you want to obtain the certification. They will conduct some test only on the final product. You can put whatever you want inside, it's not their matter. But, if you want to use some components which desn't fit the standard requirement you may have some troubles on tests except if your mission profile can help you or if you design a system to improve the function (example, you can use for a large temperature operation a component which isn't specified for if you put it in a thermal controled area)

In conclusion, note that certification of your product is now obligatory but as I've posted before, the organism may not conduct the tests or part of the tests if you can justify why (example : your product is part of a range of products, in this case the certification organism will test the baddest one regarding to the standard. The others will be certified by difference)

Regards
Stephane