You should have 4 flags. Looking out towards the field you should have 2 + 1 on the right post and 1 on the left post. For juniors you could use just 3 flags and eliminate the addition flag from the right post.
Your flags should always be tucked neatly into the post padding. If the padding is loose a roll of electrical tape can be used as strapping so that the stay in position.
The trick to positioning is to always have the ball in front of your line of vision coming towards you. For example, if the ball is coming from your left as you look out you should move to your right to keep the ball in front of your line of vision.
Generally you should try and stay 1m to 1.5m behind the line to avoid getting caught in the field of play.
For any ball dropping on the line you need to straddle the line side on tot he ball and the players.
The decision point is when the whole of the ball crosses the line. If the ball hits the goal post or anything connected to it a behind is recorded. If the ball hits the behind post it is out of bounds.
Completing a Scorecard:
The scorecard is to be completed on a quarter by quarter basis using numbers not strokes and should be continunal as per the example below.
1 2 3 4
1 2 3 4 5
7 8 9
4 5 6
10 11 12
9 10 11
This methodology will ensure that the scorecard equals the scoreboard at all times.
If cards don't match the scoreboard then the admin people may assist.
Please note: local rules and regulations take precedence over any advice provided in these goal umpiring tips.