I've been much better recently at seeing my crochet/knitting projects through, finishing them within days/weeks of starting them (as opposed to months/years!). Here I will share what has helped me (FYI, it's not about willpower)...
It's all about your thoughts before you start the project:
1. Will you enjoy the process?
Ok, so something has inspired you to make something. Do you enjoy making such items? Eg, "these colours would make a gorgeous Queen size ripple afghan"... While this may be true, are you willing to spend many hours of repeated rows? From your previous experience, have you enjoyed and completed similar projects?
2. Do you have a good reason for making it?
Amber from the Yarn junkie podcast once mentioned the feeling of being overwhelmed by yarn stores. Tell me about it! What happens when I see random yarn: "Oh this yarn would make a gorgeous cardigan". Think about it Lorraine: Do you or someone else actually need a cardigan? Is the yarn in a colour that will actually suit the recipient of said cardigan? Yes? Go for it. Line it up for a birthday. No? Step away from the yarn.
Also, I'm terrible for seeing an array of toys, eg, safari animals, and immediately wanting to see them on my own little boy's toy shelf. Knowing myself, what I really want is the finished product of a line of toys, without the repetitive work of sewing up. I remember once dreaming up a whole series of Mermaids, each having different coloured hair, different accessories. I got bored. I made 1. Now, if I want to make my son something to enjoy, it won't be a collection that just sits on the shelf to look pretty, it'll be 1 unique creature of a decent size, that he'll actually love.
Other good reasons include upcoming babies, generally wanting to give out of love, a lack of blankets when winter's coming, re-stocking your etsy shop, and among other things, as I mentioned above, birthdays.
3. Have you got (what I call) a '3-Way Compatibility' of yarn texture, yarn colour and item pattern?
This is so important, and one reason why ravelry's search options are an excellent tool. It's all very nice to see a nice pattern of a pretty pink cardigan that drapes nicely on a model too. Ok so you might make it in a different colour for yourself, but what I've found is that it's often the perfect combination of 3 things that make me fall in love with an item. So just bear in mind that it might be the shade of pink in the pattern's picture that MAKES the cardigan stand out. Would another colour, eg grey, actually suit it? Also notice the drape. Heavier yarns; those with less meterage per 100grams tend to drape nicely. A matching shade of pink in a matching yarn weight won't achieve the same effect if it is a fuzzy acrylic yarn, for example.
So, if you can say 'yes!' to all of the above, you know you will enjoy making a beautiful item that has a perfect home once finished. This is sure to bring about pro-active crafting. It's lovely to dream, and to just not care and stitch away just 'because', but if you're feeling overwhelmed with your countless WIPs, then it doesn't do any harm to be realistic too.