1) involve your colleagues: of course, you can manage your
CLIL project on your own, but it won't be as effective as with two or more teachers working together. So, if you're the Language teacher, I would advise involving one/two subject teachers (it depends on the topic you're willing to deal with: History? Geography? Science? it's up to you). And if you are the subject teacher, of course you'll have to involve the Language teacher: otherwise you will offend him/her, by apparentky teaching something they are supposed to teach (language).
2) talk about your project idea: don't keep things just for you and your involved colleague(s). Do speak with others during the official meetings: Principal, other colleagues and families need to know what's going on. They will support you in case of need, give you useful advice, or be interested in developing a similar pathway. Or - this is for parents - they will need to be reassured and to understand what's going on (let them know it won't be too difficult for their children and it won't ruin their marks).
3) choose a limited number of classes and set a reasonable timetable: for my first attempt at a CLIL project, I started with two classes, two colleagues (I teach History and Geography and I asked the English teacher and Science teacher to join me) and a series of 10 lessons. A small project, in terms of involved people and time, is easier to manage. Plus, you won't have to squeeze your brain to make up hundreds of new activities!
[and that's why I keep going :) ]