Pruning trees
Go easy when pruning trees. An established tree usually only needs some dead wood removed, but you may want to thin out the branches so more light reaches the garden beneath. Cut out weaker branches and then any that are growing immediately above or below others. Next, stand back and take a good look before cutting any more. If a tree is branching too low, you can cut out the lowest branches so as to raise the crown, but it's better to do this over a few years than all at once.

Some trees may need pruning when young to encourage them to develop into shapely adults, but it's wise to take several years over the initial pruning.

Pruning conifers
Conifers fall into two broad classes: those that branch at random along the stem (for example, sequoias, cypresses and junipers), and those that bear their branches in whorls (central growth points), radiating out from the trunk or limbs like the spokes of a wheel (for example, pines, cedars and firs).

This distinction is very important when you're pruning. Conifers with random branches have dormant buds all along their shoots and can be cut anywhere. Conifers with whorl branches have buds only at the points where the whorls arise - at the tips or the bases of new shoots. If you cut between them, there will be no growth and the cut branch will die back.

Cut only to a lateral bud or, if you can see it clearly, to the cluster of buds that mark the base of a year's growth. Don't cut into bare wood - the dormant buds lose viability when the leaves finally fall and so it won't regrow. Taxus, the English yew, and podocarpus, the plum pines, are exceptions to this rule.

Pruning conifers. The juniper, on the left, is random branching (as the arrows show). It should be pruned on the broken line. The pine and spruce, centre and right, are whorl branching (as the arrows on the spruce show). They should be pruned on the broken lines.

Pruning shrubs
Shrubs fall into two main groups: those that have several permanent branches growing from a single, short trunk (daphne and most grevilleas) and thicket shrubs that form clumps of stems growing straight from the ground (philadelphus, abelias and may bush).

Shrubs with a trunk are usually headed back (trimmed lightly just above the growing tips at the ends of branches). Thicket shrubs are thinned by cutting a few of the oldest branches right to the ground.

Large shrubs, such as camellias and the bigger bottlebrushes, can be trained into small, multi-stemmed trees by removing the lowest branches, starting when they're young and flexible.

This plant needs pruning.

Head back some branches.

This multi-stemmed shrub will look like a small tree if pruned along the broken lines.
The same shrub after pruning.

Pruning groundcovers
Groundcovers can be kept dense and low with an occasional shearing or general heading back.

Source: Gardening: A Commonsense Guide (Murdoch Books)