Communication styles are difficult to describe in Belgium due to the dual-language nature of the country.
It is probably best to look at the two language groups separately before looking at any similarities that may exist.
Flemings would tend to be direct in their speech, saying more or less what they mean in a matter of fact way. As in the Netherlands, arrogance or boastfulness should be avoided at all costs. It is best to appear low key and modest rather than giving the impression that you are somebody special. It can take longer to move from the surname to the given name than in the Netherlands and this can make Flemings appear to be somewhat more formal in approach to people from cultures where first names are the norm in business relationships.
The Walloons share the French love of rhetoric and therefore will tend to be somewhat more voluble than their fellow countrymen. Less concerned with pure logic than the French, Walloons are still heavily influenced by a well-presented case, which is fluently expounded. The way you say things carries a good deal of weight. As with the Flemings, surnames tend to be used at work — although younger managers are challenging this convention.
When in Belgium, it is probably safest to speak English even if you are fluent in French. By speaking in French you are instantly allying yourself to one particular faction. English is far more neutral and is widely spoken (especially in Brussels.)
Humour is used in business but far less frequently than in countries such as the UK and Ireland. Humour would tend to be used at the beginning or end of meetings but rarely during the serious parts of proceedings.