I started with meditation while I was at high school. The meditation sessions were sporadic and ad-hoc. I do not remember the technique I adopted in my early days.
I remember the meditation details starting from undergraduate days. Some of my engineering seniors became monks of Ramakrishna-order after their graduation. Through them and some books of Advaita publication, I picked up the flame-or-picture-in-heart-technique.
In this technique, one has to imagine the presence of their favorite person or a burning flame in the chest area. All the thoughts should be focused on the flame/person-in-our-heart. In case the thoughts wander around, it needs to be brought back to the flame/person.