Hi Baldeep,
It is the similar process how you extract data from other source systems.
There are no important steps in BW 7.3. All you have to make sure that you have data in the planning books on the source side.
Since you are talking about planning books, I am assuming it might be a full extractor.
If your load is weekly then you might have more data.. so try to make sure you have the BW modeling appropriate to your scenario.
Let me know if you have any concern.