Changing gear is a very frequent thing when driving a manual vehicle, so easy concise gear changes are useful.
Changing up and down
When changing up a gear the technique is to place the hand on the gear lever in the position ready for the change, check your centre mirror, put the clutch down to the floor and come off the gas completely, select the gear bring the clutch up to the biting point an pause momentarily than continuing to pivot on your heel to complete the rest of the clutch movement smoothly and finally reapplying the gas.
Changing down is the same. The ways of recognising when to change up a gear would be to listen to the revs of the engine building up, most cars between 1-2,000 revs is ideal unless going uphill where you may need more speed before changing to compensate for the gravity effect. Then there is to look for the speed limits, so 0mph start in first and aim to roughly change up at every 10 mph intervals so for instance second would be 10mph and third 20mph etc.