I'm a brand ambassador for a few companies now, including LumeCube, Manfrotto, TriggerTrap and CoverUp to name a few. These were all born out of my Instagram account. Over the past year my Instagram has gone from around 400 followers averaging 10-20 likes per post to 14,000 followers with an average of 1,500 - 2,500 likes per post. That's the major reason I get asked to be a brand ambassador. I can consistently offer high levels of organic interaction. Pretty much any product I post a picture of Will gain a high level of exposure. Should I post multiple posts then that increases dramatically. For example with Xiro (The company that make my drone) I have accumulated over 80K likes in the past 8 months on images I have shared that they're tagged in. That's an incredible reach creating great exposure for them. In addition to my high interaction levels, due to my profession I can also create high quality photographic and video work for them. This will either be sent directly to them for their own use or to further the exposure of the images I share.
This isn't obtainable for everyone. Getting my Instagram to those levels was hard work combined with luck. Also not everyone has the ability to shoot the same kind of content that I do. What you Do have is the ability to build your social media presence and do so in a way that give you a value to companies. You see accounts on Insta or Facebook with 100k+ followers and yet if you look at their posts they average 50-200 likes per post. It doesn't matter how many followers you have at all, what matters is how many people are interacting with every post you make and how relevant they are to your 'style/ theme'. My page is primarily personal. I showcase shots from my days out with the family, exploration shots with my drone, BTS from my shoots and then straight up family shots. This means that my account is very organic. I'm not pushing paid content down peoples throats i'm just being 'me'. Companies I represent are relevant to that in order to fit in with my page. Find your niche and focus on building a following of relevant people to that. Once you're consistently producing great levels of interaction there is no harm in contacting companies to see if they want to work with you.
At first companies won't find you, you need to find them. It may be companies you already admire. Reach out to them and explain you love their product and would use their products (Or already do!) and see if they're interested in collaborating in exchange for a discount or a freebie. You won't get responses all the time but when you do you have an 'In'. They may say you haven't got enough interaction for it to be worth their while yet. When you do get to that level down the line you now have that contact point to reach back to and showcase your growth.
I personally don't work with companies I wouldn't/ don't already use. I don't want my account to be littered with irrelevant posts. However if there's a company that I love like CoverUp i'm more than happy to help gain some exposure for them as I love their products and i'm sure a lot of my followers would as well.
This isn't something that happens overnight and isn't really what I set out to do with my social media but a cool bonus that has helped me gain some fantastic contacts and awesome gear!