I think there is s story of Guru Nanak who joins a rich man in a Mosque for prayers and half way through Guru Nanak starts to laugh. When quizzed by the rich man why he laughed, Guru Nanak said you were not thinking about God but about a business deal that you did yesterday.
One of the most toughest part of being a Sikh is being a "Householder" i.e. not withdrawing from from life and becoming an ascetic but being part of society and despite being surrounded by the 5 thieves still being able to live life.
The 5 thieves are like the Hindu analogy of the horses pulling a chariot. If they are allowed to run riot, the chariot will over turn, and not go anywhere. If you manage to control them then you can go in the direction you choose rather than the horses. They will always be there, but it up to you to control them.
How to we control the wandering mind? We ask God to remove that particular thief from our mind. If we try and do it by ourselves we will fail, because that is self will and even the strongest of wills cannot control them. Aim to be a Gurmukh, and allow God to control them. This takes time, and will never be perfect (unless you are a Saint), but Sikhi does not ask for perfection, but merely a willingless to be Godwilled (Gurmukhs), rather than Selfwilled (Munmookh).
On a practical side, Sikhi talks of Miri and Piri, just as teh spiritual side of development is important, so is the mental and physical, so doing mental excersises (reading, writing), and physical activity (martial arts, excersise) will help concertration.
