I'm surprised that Belgium football team is standing No.1 in FIFA World Ranking. They have never won the World Cup. What made them standing ahead of Germany and other more well known teams?
The FIFA world ranking is calculated based on results from all matches a team play: Qualifying matches, friendlies and championship matches. Matches from the last four years count, and it's weighted so that more significant matches and recent results count more. Also your opponent is weighted so that higher ranked opponents gives more points for a victory.
You can read more about it here: wikipedia on FIFA world ranking
So why is Belgium on top? The simple answer is that they have gotten the best results against fairly good opponents. If you look more at their results you will find that they have won their two last qualifying groups. They only lost against Argentina in 2014 WC and have performed well in their friendlies.
At the same time there is no doubt that the ranking could be exploited by carefully selecting friendlies to get the highest possible ranking. I'm not claiming that Belgium have done this, but it happens and proves the difficulties in making a ranking.