I wanted guidance / tips and tricks to join two balsa pieces at 45 degree angle.
Please guide me to do it with accuracy without leaving any gaps in between.

Thanks,
 

You will need a block of wood with fine sandpaper stuck on. Use rubber solution (called Fevibond I think).
And a drawing board on top of a table.
Place the wing half at the edge of the table, and prop up the tip to the required height.
Preferably tape it down.
You can see a small width of balsa on the top edge. (Pic #1)
Place the sanding block on the table top, touching the edge of the drawing board.
If the block has square edges, the sanding surface will be perpendicular. (Pic #2)
Run the sanding block a few times in contact with the edge of the drawing board to bevel the inner egde of the wing.
Repeat with the other wing.
You should get a joint like this (Pic #3)

Hope this helps.
Regards

@KK Iyer : Thank you sir.  That's a a good technique.

What's techniques other flyers use ?
Can we have more suggestions?

Here’s a useful tip.
Make tiny pinholes in the surfaces to be joined.
Use 5 min epoxy (Araldite Rapid/Klear), but not too much.
You’ll get a strong joint without needing a dihedral brace.