Well, as long as there are enough food and drinks, some very loud, hip music, and some color lights, you are good to go. Try covering the light bulbs with orange and black translucent paper, that would make for low (blackish) and orange lighting that would look halloweeney. Also, cut out paper bats and hang them from the ceiling. Besides that, do scary things, play the paper, fake version of the ouija, and move the pencil yourself so that it looks like spirits are talking to you, tell ghost stories, watch the saw movies, or at least play them for people to watch them if they want to, and chill out. You may also want to make a costume contest. Give out candy as a prize or something. Or try and scare the children that come by treat-or-treating. Idk, just have fun.
Also, a funny thing would be to have all of your guests and you go treat-or-treating yourselves and look at the neighbors´ faces when they see a whole lot of big people asking for candy.
You can also take some fairly hot chiles and cover them with chocolate ad put them in a bowl. People will eat them and it will be fun looking at their faces. As for other foods, just have oogey stuff and things that smell nice but look disgusting. Or just order pizza.