1) what are the general conversion rate ?
There isn't a general conversion rate , it all depends on your website, the quality of value you are giving, the kind of brand awareness you built and the kind of keywords you bid on.. Going further, I haven't sold electronics yet but from what i have been hearing is for tablets big brands gets near 2.5% Conversion and for smart phones below 1%.. Well thats about big guys.. So someone with a brand new start it will go lot worse..
If you have some money to burn, run your ads and find out yourself. If not note down your margin per order, note down the CPC you are going to pay and take 1% conversion rate as example and do your math. Most probably you wont be profitable but lets see.
lets say you are paying 50 cent a click (Not gonna happen in electronics but lets take the lowest) and your conversion rate is 1% (Just taking a higher value) you are gonna pay 50$ for a single sale. For a 200$ tablet if you are not making 30% margin after removing payment fees (3-4%, shipping fees if any) and so on, you are not gonna even break.
again those were just some numbers, I strongly recommend you to burn 200-250$ in ads and learn that adwords is not your way to go and stick to other traffic sources (There are traffic sources which converts and are cheaper).
2) how i can maximize my conversion rate ?
Get some convertions first, you will know what you are doing wrong yourself .. More on this later once you report back