If Q is positive, then the electric field points radially away from the charge. If Q is negative, then the electric field points radially towards the charge. We obtain the electric field due to a collection of charges using the principle of superposition. The direction of the field at any point is given by the direction of the field line, while the magnitude of the field is given qualitatively by the density of field lines. The magnitude of the field and the density of the field lines scale as the inverse of the distance squared.
Field lines start on positive charges and end on negative charges.
Lines are drawn symmetrically leaving or entering a charge. The number of lines entering or leaving a charge is proportional to the magnitude of the charge. No two field lines can cross since the field magnitude and direction must be unique. The figure below shows the electric field lines for a system of two point charges. Thus, the one on the left is 4 times larger than the one on the right.