To make the Kubera Mantra more effective some rules we should follow.
मनुजब्राह्म विमान स्थितम्
गरुड रत्न निभंनिधि नायकम्
वर गदेदघतंभजे तुन्दीलम्
Manuj Brahma Viman Sthitam
Garud Ratna Nibhamnidhinayakam
Var Gadedadhatambhaje Tundilm
Meaning:- Sitting on a flying machine in human form, like the great eagle, owner of all wealth, adorned with a crown,blessing hand and holding a bludgeon, O huge Kuber, I bow to you.
Often, after completion of daily puja a Mantra pushpanjali i.e. the bouquet of flower of Mantra is offered and we solely pray lord Kubera, the Vaishravan to give us every earthly good things:-
कुबेराय वैश्रवणायमहाराजाय नमो नम:||
Kuberay Vaishravanaymaharajay Namo Namah:
He will certainly bestow wealth upon you. However, you should not let this monetary advantage go to your head.
It is the mark of the demon Kali which clouds your mind and fills it with arrogance by inflating your ego.
You should stay as humble as possible. Otherwise the Mantra will be of no use!