1
I have tendency to worry too much.
I have a tendency to worry too much.
Tendency is a singular countable noun in this expression, so use a: have a tendency to + infinitive.
2
My brother has a tendency of arriving late.
My brother has a tendency to arrive late.
Use a tendency to + infinitive, not a tendency of + -ing: ‘She has a tendency to speak too quickly.’
We can also use tend to + infinitive: ‘She tends to speak too quickly.’