Firstly, searching for mushrooms isn’t a race - walk slowly, stop and look around. Mushrooms can be hard to spot at the best of times without actually stopping to look. Beginners are particularly bad at seeing even what is directly in front of them until they’ve "got their eye in." Your approach to searching can be a random wander or a systematic scan - depending on your personality or the openness of the ground you’re searching.
When first starting out mushroom hunting its usually best to limit your self to a few common and easily identified species. As you become confident with these gradually extend your list. If possible, your first trips should be with a more experienced mushroom forager that can show you the ropes. There are many mushroom forays organised by local foraging groups or mycological societies which are a good starting point. There are also commercial courses where you pay to attend and get expert tuition.
So you’ve spotted a fungus. You’ve now got decide whether its edible. Use your field guide and systematically check all of the features of the mushroom. If they all match the descriptions of a mushroom your list, well done, pop it in the basket. You might consider taking those you’re not sure of home for closer inspection, but keep them separate from your main collection.
With your mushroom safely in your basket search very carefully in the immediate area for others. Many species grow in groups or rings so others may to be close by. Even if you don’t find anything in the immediate area, still pay close attention to the area around where you made your find. You’ve found one mushroom that liked the conditions there, others might too.