Based on the title of this tread and the description, I'd say this is definitely not a workflow related question. What I understand from Ashish's description is that:
1. Users browse to the newForm.aspx page of list
A to enter new data to the list
2. Enter a value in the "Title" field
3. At this point, values of other fields should be populated automatically
a. The values that will be populated, are coming from List B, where the "Title" fields from List B matches the value in the current list's (List A) "Title" field.
Ashish: Please advise if I've misunderstood what you are trying to do. You can only run workflows once you saved the data, not while you are in the process of doing that. There are different approaches to this.
I don't know all of your requirements, but I'd recommend you not to populate data from the other list. Because you'll end up having duplicate data in both lists and later you'll need a workflow to synchronize the data when List B changes as per the above example. What you can do is create a Lookup field/column in List A and connect it to List B. This will create a link to List B for each records in List A.
1. Add a "onchange" event handler to the "Title" field
3. Set the values of fields in the newForm.aspx page accordingly