not sure what you want to hear, but here's some common sense stuff:
1. Make sure you always pay your rent, and preferably do so on time, and get a written confirmation that you did so. I didn't have much of a probleme to find a new apartment once I put my mind to it, but I can't say the same about the other homeless people I've met who were turned down by landlords all the time because the reason they ended up on the street was that they got behind on their rent payments.
2. Extremely useful items to have around:
a good iso mat
a warm sleeping bag that holds off rain
if you can make money on the internet (translation/programming etc.) make sure you have a small notebook/netbook
a multitool/pocket knife
3. There are cheap hostels where you can sleep for less than $10 per night. Not being much of a traveller, I didn't know this at first.
4. There are also businesses that let you store your stuff for a small fee. Very useful.
5. Don't underestimate how cold it can get at night during spring and even summer, especially in the last hour or so right before sunrise. I mostly slept during the day, while it was sunny, which is also safer in terms of not getting your stuff stolen. During the night, I would either walk around or, when I was in a city, I would hang out at McDonald's and mooch on their free wifi.
6. You can eat dandelions and a bunch of other plants you might never have expected to be edible.
7. I know this is kinda taboo on here, but I got a few nights of good sleep on a proper bed by picking up overweight or otherwise desperate-looking girls, having sex with them and sleeping over at their house.
8. When you're walking around on the countryside, feel free to ask people for a bit of help, most folks are more than happy to help you out with water etc., so long as you're not too dirty (which can be hard when you're not in a city or near a reasonably clean river or lake)
9. Assuming you don't have a car: If you're in a city where you're planning to stay for a while or even settle, it's worth buying a monthly ticket for its public transport system even when you're pretty short on cash.
10. Large non-commercial public places like universities and airports have bathrooms where usually nobody will mind if you use them to shave and so on. There usually aren't too many of those in any given city though and restaurants tend to charge you a fee for using their restroom, so make sure you keep an eye out for places (e.g. shrubbery, public parks, woodlands just outside the city) which grant you enough privacy to pee, defecate and masturbate, respectively.
11. I did come across one exception, and it might be different in your country, but in general, homeless shelters are disgusting hellholes. I preferred sleeping outside, where it was cleaner and safer (might have something to do with the fact that I was never homeless during winter, though)