The first question would be, what sort of a ritual are you looking to do? Are you conducting a celebratory ritual whose sole purpose it to honor the Gods or the turning of the Wheel of the Year? Or are you looking for a ritual which has a magical aim as its purpose? The two are somewhat different and may require different answers.
It is perfectly possible to simply conduct a ritual completely within your head as a sort of meditative process. This works better for a celebratory ritual, but could be used for magical purposes as well. One simply visualizes the altar and tools as if they were actually in front of you and then manipulates them with the mind while moving the energy required. This is a bit of an advanced technique for someone just starting out, but it can be learned with practice.
Another way to look at this is to understand what the tools on the altar represent. Candles obviously represent the Element of Fire, while incense typically represents Air. If you can't have incense, what else could you use to represent the Element of Air? Feathers, birds, clear crystal, the color white/silver, fans, etc can all represent Air on your altar. As for the Element of Fire, you might either find unscented candles or try another representation such as fire stones like ruby, opal, and garnet; red/yellow flowers, dragon figures, a red candle (even unlit), etc. Get creative with your representations. Consider what each Element represents to you and then use the item you feel means "Air" or "Fire" in your mind.
If you're looking at doing a magical working that involves burning candles you might want to consider an alternative way of doing the spell that doesn't require them. You might want to look at my blog post on cord-magic as a possible alternative that would work in your living situation.
Does this help? If not tell me where you are having problems and I'll try to help.
Paulina, you might also consider taking your ritual outside, if there's a safe, private place you feel comfortable going to. What better way to honor the God and Goddess? :)