I think learning radicals of kanji is the nearest way to learn kanji. Because kanji is made from combination of the radicals and when you learn 3 and 5 radicals, you will get 15 (3 x 5) kanjis at most for example.
I was wrong. I have just found I had been wrong.
I found the list of kanjis for each grade of elementary school defined by Japanese government. Here is the list for first grade to 4th grade.
for the full list, access this URL: 別表 学年別漢字配当表：文部科学省
In this list, look at the first 80 kanjis defined for the first grade. Most of these kanjis has no radicals or the kanji itself is recognized as the radical.
Therefore, I understand it is no use to learn radicals for learning first 80 kanjis.
To understand and learn these 80 kanji, refer to the table I made : First 80 Kanjis