it's not good idea to set low transaction fee,, you can wait long time to receive money.
Actually the mempool is kind of 'empty' at the moment. You can view it here:
https://jochen-hoenicke.de/queue/#1,24h.
Currently transactions with a fee as low as 10 sat/B get confirmed in the next block.
Even fees with a fee of 1 sat/B are getting confirmed within a few hours max currently.
we will start seeing fees approach the minimum even for high size transactions.
The fee is usually measured in [sat/B] (satoshi per byte).
The actual fee for a transaction is then dependend on the size. But the
fee rate (sat/B) is the same for small and big transactions.
To be honestly, i don't think fees can go much lower than currently. With the LN getting developed and also used/accepted we will see a growth of bitcoin usage in general.
Together with the LN i think fees will kinda stay at the same level. In the long term, of course, fees should rise again. Even with closing channels only once per week (or month).
The increased adoption will drive the fees higher again.. but i don't think we should reach the fee level of a few months ago (1000+ sat/B) again.
At least not if there is no spam attack. SegWit + LN are awesome regarding short-/midterm scaling.