You can't force deities to work with you, however you can pray to them and ask for help with something and place an offering as thanks, don't be rude because they hate being called upon without a thanks.
From my understanding this fully depends on the deity. For example, it wouldn't make sense to call on Demeter (a goddess of fertility) for help w prosperity/income. Generally, anyway. Also, what would qualify as a good offering will depend on the god/goddess.
There are some eclectic traditions who pull deities from different pantheons to work with/worship. I don't do this myself but don't personally have a problem with people who do, but you may run into others who think this is not ok. The best way to figure out who you'd be best able to work with is to research different pantheons and see if anything reaches out to you. If you do find a deity who seems to be speaking to you I would look up appropriate things to ask of them and appropriate offerings to give in response before initiating any kind of interaction.
Deities are forces not to be trifled with, and if they don't want to work with you, they simply won't. You're really at their mercy in that respect. but if you want to add that to your practice it's possible to work on developing a good relationship w a deity or pantheon of deities.
that being said, as a disclaimer it's entirely possible to work magick without working with deities (many people don't), and I don't pretend to be an expert since I am still researching who would be a better fit for myself. This is just my understanding of interacting with deities in a respectful manner.
If you want to work with a deity, develop a relationship. The best first step is prayer. Prayer isn't asking a deity for something, it's starting or developing a relationship. In Theurgy (God work), prayer is an important first step and theurgy itself is not possible without prayer.
An example would be using something like an Orphic hymn to praise or speak to a deity. You are essentially attuning to the deity and encouraging their presence within and around you.
There is a really excellent book on working with Deities called "Devoted to You" by Judy Harrow that discusses making and maintaining a relationship with a Deity or Deities. That would be an excellent place to start.
However, perhaps the best place to start is by reading the mythologies of various cultures and seeing which pantheon appeals to you most. Then if there is a God or Goddess within that pantheon that seems one with whom you would like a relationship, go ahead and create an altar to them. You can make offerings to them at that altar, such as incense, food or drink and ask them to look upon you favorably.
There's an excellent article to help you along with this at http://gleewood.org/seeking/doing/relationships-with-deities/
