How should I prevent the quality of my game from declining? So, I was a very good player 4 years ago and then due to academic commitments I had to discontinue playing chess. Now, I want to start again but I seem to have lost the old skills and it seems that the quality of my game has dropped very much. I want to again start playing but I don't know where to start from? Is it advisable to start again from scratch as that will take a lot of time? Should I just focus on playing more games? Any pointers or suggestions please?
I have always found the fastest way to get rid of some rust to be tactics training. 

I would recommend two steps:

First you do a lot of relatively simple exercises, like game typical 'mate in two' (not chess problems, those can be quite difficult). This will remind your brain to automatically spot the easy stuff and reduce the probability of really bad blunders. You can go through the same positions several times.

Then you do some hard problems with something like 15 minutes per problem, here every problem should be new to you, you should sit down with a clock and write down your solution. This should get you back into tournament shape. 

In my experience this works a lot better than playing blitz online. Playing long games seriously should have a similar effect, but I usually want to get back into shape before I play a really serious game.