All ritual, at its heart, should serve the dual purposes of honoring the Gods and of opening us to Their blessing. It should also allow us to be aware of and reflect on our connection to those Powers and our part in the natural and cosmic cycles. It is said, although I can't lay my hands on the exact reference right now, that the ancient Druids believed that their rituals were a perpetual act of creation that kept the cosmos going; I like to think that even today our rituals help keep cosmic order, if only because it nurtures my own feeling of connection to everything.
Now personally I use several different ritual styles, depending on context. In public rituals I tend to use a more general neo-pagan format becuase it is the most accessible to the most people, and my community is comprised mostly of diverse neo-pagans. I have found that going with what people recognize and are familiar with creates the best results for the participant in an "open" public format (not that I don't work in some of my own bits, like having a public group walk between 2 candles representing bonfires during a Beltane ritual). I'm perfectly comfortable using this format myself in any of its variations and I believe that public rituals should be based in what the group connects best with. I am out there, after all, to serve my community, not myself. Other people have their own views on the subject, of course, this is just mine.
Now with my kindred we tend to use a basic blot structure. Sometimes we use the hammer hallowing beforehand, sometimes we don't, but we always start by hailing the ancestors, land spirits, and Gods, pouring out offerings from the horn to each. We go around after they are hailed and we each say we want or need to about why we are gathered and may make additional offerings. When we have all said as much as we feel we need to we take the collected offerings out and pour them onto our outdoor altar space, called a ve, while thanking the gods and spirits for their blessings. Then we feast, usually a pot-luck style meal together (some of this food is also offered later).
Now as an Irish pagan and Druid when I do rituals its usually just me, or me and my children. I try to follow a basic recon-style approach, but I have the freedom to improvise a little bit as well, even within the set structures of the specific Traditions I work in. This is just a basic outline for home rituals, and this is only the way that I do things although it reflects my understanding of recon style ritual and some general principles behind the ritual style of the groups I belong to (basically this is my disclaimer that I'm not trying to put this out there as any sort of set ritual format for anyone but myself). Of course the groups I belong to do have specific set ritual structures, but that's not what I'm writing about, nor is it necessarily my place to do so.
I start off by burning either juniper, vervain, or an incense blend I make that combines several herbs and woods used historically for cleansing. I like to sing, so I usually sing something that creates a feel of ritual or sacredness - at the moment I've been going with the song "There Is No Time"; it's not historic or even tradition specific but I like it and I feel it works to create the feel I want to start off with. While I sing I walk three times sunwise around my ritual space, sometimes carrying the incense. After this I acknowledge the three realms and the three Powers associated with them; sea and the ancestors, land and the daoine sidhe, sky and the Gods. If a specific holy day or occassion is associted with one or two deities then I will only call that one or those two when calling the Gods. I invoke* each Power and make offerings to them apprpriate to their nature and which are environmentally safe. For example I might offer incense made from organic local plants, I might light a candle, I might write a poem and then burn the only copy during ritual, I might burn butter or olive oil, I might pour out pure water, milk, cream, or (rarely) alcohol, that sort of thing. After all the guests have been invited to the party, so to speak, I will talk a little about the purpose of the rite, perhaps read a poem or blessing - often something traditional from a source like the Carmina Gadelica, sometimes moderninzed or made pagan. If I know any appropriate songs I would sing them now. Some specific holy days like Beltane or Samhain have particular actions or activities that might occur, while others are more general. This is when any special activity or prayers would be done, followed by divination to assess if the offerings were accepted and the actions effective. Assuming the divination looks good and nothing has to be redone or "fixed" then the main body of the rite is finished. The gathered Powers are acknowledged and thanked for their presence (except the daoine sidhe, as I have a superstition about never saying "thank you" to them I ask instead that there always be friendship and peace between us). The energy of the ritual is grounded as an offering to the earth, and any physical offerings are poured out on the ground or left outside on the outdoor altar (the ve does double duty here). Usually this is followed by feasting.
There is a lot of similarity between the heathen style ritual and the Irish/Druid style one, but the heathen blot tends to be simplier and more straight forward, an honoring of the Gods and Spirits. Druid ritual is a bit more about energy and the altered consciousness that comes from connecting to Powers outside ourselves, in my experience. And public ritual should create some feeling of connection and experience while honoring the Gods. All rely on a basic structure blended with unique elements and a person's willingness to be open in giving (making offerings) and recieving (accepting blessings/experiences).
*invoke, despite modern pagan misconceptions of the word, means
"1. To call on (a higher power) for assistance, support, or inspiration
2. To appeal to or cite in support or justification.
3. To call for earnestly; solicit" (http://www.thefreedictionary.com/invoke)
I use words based on definition not popular perception or urban-legend style meanings.