You can never have that 'first love' feeling back because your relationship is moving towards a more mature love.
In order to introduce more excitement, add laughter to your lives. Evolutionarily speaking, laughter is an attractive move, rising certain chemicals in the body to generate a mating response, a familiar response, and a protective attitude. In other words, it strengthens the bond.
When things are comfortable yet lacking in romance, do something out of the ordinary. Bring flowers, cook a meal, get down on one knee and recite a short love poem (Shakespeare is the most recognized).
Take them out on a date, and behave shyly, coy if you will. Ask them questions on this date that you didn't ask on the first one.
Go dancing, and not to a club with lots of noise.
When you are first dating everything is new, exciting. To bring back similar feelings is to do similar activities.