In subsidiary alliance ,the british posted their own army in the state .the army had to be maintained by the ruler.a british resident was also posted in his court

the ruler could not employ any european without consulting the english, nor could he deal with any indian ruler on his own.
In 1798, this one general, named Lord Wellesley introduced a programme to protect an Indian state to establish British Supremacy in India and remove all traces of French Rule. The Nizam of Hydrabad was the first to accept it.

But, it had some terms and conditions. The ruler who accepted this alliance had to:

1) Maintain British troops at his own or cede some territories for the purpose
2)Expel all non-english foreigners from his state
3)Allow the British to supervise his relations with other Indian states
4)Accept a British resident in his court. The resident would interfere in the state's matters to promote the company's interest.

The first ruler who didn't accept this alliance was Tipu Sultan. His refusal resulted in the Mysore Wars.