Besides the basics (which are listed here, for those curious: http://bills-pokedex.tumblr.com/post/152002181001/how-to-take-care-of-a-ralts-please ), perhaps the most important advice I can offer is, strange as this might seem, always be aggressive about self-care. As in, care for yourself, rather than your ralts. Psychic-types can be quite difficult to work with, especially for those with negligible or latent psychic abilities (or perhaps none at all, if you don’t subscribe to the idea that we all have some baseline psychic ability). At first, a psychic pokémon may inadvertently use their abilities on their own trainers, which may be traumatic for a human with little experience in telepathic blocking. Moreover, as you grow closer to your pokémon and your pokémon grows more powerful, your psychic link will grow stronger as well. Not only does this mean psychic blocking will be imperative at that point, but also, if you don’t train yourself, your pokémon’s use of its powers may take a negative toll on your physical health. At best, that means you’ll feel exhausted after battles due to your partner literally drawing strength from your bond with it. At worst, it will mean chronic debilitating migraines or (rarely but possible) brain aneurisms. Or, well, battles become more dangerous because your emotional state may disrupt your pokémon’s concentration, thus increasing the risk that it will lose control of its abilities and seriously injure you or those around you. Either or, really.
Thus, it’s important that you build up psychic tolerance early. Train with your ralts frequently so you can get a sense of its telepathic signature (or the spiritual aura it emits when using its abilities). Meditate at least once a day to teach yourself how to ground your mind and clear your thoughts at a moment’s notice. Pick an idea or memory that makes you happy and learn to focus on it when you feel your pokémon entering your mind. Learn to build a psychic maze (that is, a series of thoughts designed to distract and confuse psychics) as further defense.
And above all else, take care of yourself. Always get a full night’s rest before a major battle, eat right, and keep your energy up by exercising daily. And of course, also be sure to train your ralts to control its powers and know when it is and isn’t appropriate to use its abilities on you. This all is particularly important for the ralts line, as its powers are more based on the reading and manipulation of others’ thoughts than most psychic pokémon, so I wish you the best of luck in training yourself.
As for other companion pokémon, strangely, dark-types are perhaps the best choices. These are immune to a lot of ralts’s abilities, which means ralts can associate with them without the stress of holding itself back. They also make for excellent sparring partners later on in a ralts’s life, especially if yours eventually becomes a gallade. Alternatively, other psychics can work together with your ralts (meaning training becomes far easier), and therapeutic pokémon (such as those that can use Sweet Scent, Aromatherapy, or Sing) can keep your ralts calm and in control, even in high-stress situations (such as urban environments).
Good luck, and congratulations on the new addition to your family!