Multiclass Monks add the BAB of their non-monk classes to their flurry of blows, and gain an addtional attack when the last attack is +4.
For example, your Monk 10/Cleric 6 FoB would be +12/+12/+7/+7/+2.
In any case, flurry of blows is Monk lvl + Other BAB, then additional attacks when last is +6, and additional attacks at 1st, 8th, and 15th monk levels. Lastly, everything is -2. It's all written there in the Flurry of Blows description.
Flurry of Blows (Ex): Starting at 1st level, a monk can make a flurry of blows as a full-attack action. When doing so, he may make on additional attack, taking a -2 penalty on all of his attack rolls, as if using the Two-Weapon Fighting feat. These attacks can be any combination of unarmed strikes and attacks with a monk special weapon (he does not need to use two weapons to use this ability). For the purpose of these attacks, the monk's base attack bonus from his monk class levels is equal to his monk level. For all other purposes, such as qualifying for a feat or a prestige class, the monk uses his normal base attack bonus.
At 8th level, the monk can make two additional attacks when he uses flurry of blows, as if using Improved Two-Weapon Fighting. (even if the monk does not meet the prerequisites for the feat).
Assuming you decide to read this as it's printed without inserting any preconceptions into it, your BAB as a Monk 10/Cleric 6 would be:
Without FoB: +11/+6/+1 (+7 from Monk, +4 from Cleric)
With FoB: +12/+12/+7/+7/+2 (+10 from Monk, +4 from Cleric, -2 for TWF)
Multiclass Monks add the BAB of their non-monk classes to their flurry of blows, and gain an addtional attack at -1 when the last attack is +4.
For example, your Monk 10/Cleric 6 FoB would be +12/+12/+7/+7/+2.
In any case, flurry of blows is Monk lvl + Other BAB, then additional attacks when last is +6, and additional attacks at 1st, 8th, and 15th monk levels. Lastly, everything is -2. It's all written there in the Flurry of Blows description.
Monk: The monk rules for flurry state, "For the purpose of these attacks, the monk's base attack bonus is equal to his monk level." How does this interact with BAB from class levels and racial Hit Dice? Does a multiclassed fighter 19/monk 1 flurry as if his BAB were only +1?
A monk using flurry treats his BAB from monk levels as equal to his monk level. He still adds BAB from other sources (such as other classes or racial Hit Dice) normally to this total.
So a fighter 19/monk 1 has a normal BAB of +19. When he flurries, he treats his monk BAB as +1 (for his 1 level of monk) and still gets BAB +19 from his fighter levels, for a total flurry BAB of +20.
—Sean K Reynolds, 09/10/10
So, a Monk 10/Cleric 6 would have a total flurry BAB of +14
Often confused - language was updated in the Fifth printing.