Time, being helpful, offering advice - but don't be a fool
I didn't need to read loads of books by famous people in business to be told how to treat people, I've always done the odd job either for free or in return for something else or trade or even just because I knew the person needed my help and if they didn't get that help they couldn't move on and seize an opportunity. Somethings are also down to time, at that time that person might really need you and in months or years to come, they may return the favour.
To a point! none of us want to be used or taken for granted but I think I've worked enough years in business to spot the difference, and if I get it wrong, well I've tried and the risk was mine. But don't do it too often!
You can also never know who one person in business might introduce you to. Networking doesn't always pay the same day, the same month or even the same year but helping one person might just put you in contact with someone who does turn your world around, provides you with more work or in turn introduces you to someone else. You just never know. It's happened to me several times and I think it's about to happen again.
But don't be a busy idiot, do think hard about who you chose to support, don't go in for promises 'oh when this comes off I'll pay you, when I get this deal it will be great for both of us' decide to do the work or walk away and don't get caught up in the promises (it can lead to resentment and bitterness), if it comes off the risk has paid off, if it doesn't that's what taking a risk or a punt on someone is about and you only have yourself to blame!