Well, I've only actually used one real ouija board in my entire life. It was store bought. The rest of the times, I used my own made one.
From experience, I know that ouija board sessions dont always end the way you expect them too. So take any precautions you have too, but the best one would be not to do it at all. The last time I used a ouija board, it ended wrong, and I never touched one again. So, I'm not quite sure if thats the best idea. Overall, I dont encourage it.
But, if your still adamant for doing it, I could provide some tips.
No symbols (or atleast not that I know of) are required to ocntact anyone or thing. They come on their own, and nothing really attracts them more than another thing will.
Blessing the ouija board may take away performance of the board. So if you want real results, I dont suggest blessing it. Alot of the time, people think it will make the baord safe. But trust me, nothing about the baord is safe, and nothing you ever do to it will ever make it someting it's not.
But, placing a few white candles by the board while during your session will protect you. It doesnt garuntee safety, but it will help take away some of the evil if you encounter a demon or spirit that wants to do harm.
Now, when actually using the baord, there are a few rules that you must follow.
1) BE KIND! The spirit will not appreciate it if you are rude or if you humiliate it.
2)Only one person may talk. Throughout the whole session, have a speaker, someone else who places their hands on the planchette, and a writer.
3)When you have contacted the spirit, the second thing you should ask it (the first being 'is anyone here?') is 'are you from the sun or the moon?' I'm not sure if alot of people know this, but asking the spirit if they're good or bad angers it, and you must never ask that. Instead, asking if they're from the sun or moon will determine if the intentions are good or bad. The sun being good, the moon being bad. If they say bad, tell them goodbye immediately and wait until they move the planchette to the goodbye lettering.
4)Try not to get too personal. If you think the information you want to know is a bit too personal, it will anger the spirit. Dont ask anything like that!
Other than that, I'm not sure what else there is to say. Good luck, I guess. Hope this helped :) Ask me if you need anymore information!