Socialising your puppy is an important process and one that should begin from the moment you get him home. Introductions to as many different people, environments and activities as possible early in life will help him develop confidence.
It should also help you feel more confident in handling in these new situations. Make sure that you are as comfortable and relaxed as possible in new or difficult situations so as not to resonate any negative energy to him.
Remember that they will be looking to you for support and guidance, as you are their pack leader. Every action you make will be transmitted to him. For example, if another dog approaches whilst you're out walking and you tense up or hurry away, your dog will perceive the other dog as a threat and react accordingly.
If this pattern were to occur regularly then he would begin to expect this and pre-empt you by reacting aggressively immediately upon sensing another dog, it is in this way that bad habits are formed.