The first step is a simple protection ritual. Light a candle or a lamp, say a prayer to whatever deity you believe in or follow to bless your journey and guide you to your spirit guide with no harm come to you. This does not need to be complex, a simple blessing and asking of protection will do fine. This is done because you are, after all, reaching out to the spirit world and asking for guidance, and don't want to risk getting a guide who is not there to help you.
The second step, then, is meditation. If you don't know how to do this, begin by teaching yourself the basic techniques, and find one that works for you. There are countless tips on this site, and if you can't find something here that works, you can always turn to google for help. Try to find a peaceful quiet place in your mind where you can do work while meditating. For me, it is a peaceful forest grove. For you it may be by a stream, in front of a fire, your childhood bedroom, a tree fort, complete blackness...the possibilities are endless, it needs merely be somewhere you can envision and retreat to where you can shut out all other thoughts and focus on a single goal. Once you reach the ability to do this and sustain this for a good period of time, move to the next step.
The third step is asking. Sounds pretty simple, right? That's because it is. Ask your spirit guide to appear before you (and be polite, this is someone who will be helping you, not someone you get to order around like a slave!) or appear to you in some manner. You may get it right away. Or, you may sit there and nothing happens. Maybe when you fall asleep that night, you dream of your spirit guide. Or perhaps, nothing.
If you find your spirit guide right off the bat, congratulations! If not, the next step is simply patience. Spirit guides will come on their own time, when they believe you are ready. You may realize, after time passes, that you keep seeing the same woman or man in your dreams, or hearing the same voice when you meditate or perform rituals giving advice. Once you figure it out, don't be afraid to ask what their name is, what they can teach you, what their purpose is, etc. They are your guide and guardian.