You already know that dipping in and out of social media has minimum impact. If you only post or Tweet or update your status once in a while you'll certainly gain little business advantage and only chance connections with people you know. To consistently show up on your target market's radar, you really need to be a frequent poster. Beyond frequency, however, you will gain even greater benefit if you post content types that indirectly but consistently support your business.
Think of this question: What type(s) of information might my target market want to know? Particularly if this information changes often, if you post regular updates on social media, then your hope can be that people in your target market will discover and regularly return to your page or look for your posts.
It helps a lot in choosing the types of content to post regularly when you post information that matters to you, too -- that way you'll be motivated to look it up in the first place plus it can implicitly build your relationship with your followers or friends.
For example, as a real estate agent on the southeastern North Carolina coast, I'd like people who live elsewhere to understand how great our weather is. I also like to let folks know about the depth and variety of arts and cultural activities in our area and the types and frequency of business networking events. All of the above matter to me -- I love our weather, I'm interested in the arts, and I attend networking events. It makes sense to me that if I connect with people both locally and from other parts of the world who share my interests, I not only put out some common points of personal connection but I also might attract potential real estate clients.
So, every morning I post a short summary of the local weather report (often with a comment about going to the beach), I post a link to the day's entry in a locally generated arts and cultural event calendar along mention of one or two events that strike my curiosity or interest, and I post notes about upcoming business networking events. I also put in the hash tag #ilm in the posts - sorry for that techie bit, but it's a way for people who track our area by such markers to find my posts.
To break this example down just a bit further, the purpose behind my daily posts are to appeal to other people who appreciate nice weather, are interested in the arts, and who find value in business networking events. Doesn't it make sense that those people could be in my target market? Notice, however, that while those three topics relate personally to me, and to my business, that I'm not asking people to buy or sell real estate and not even mentioning the company name. So there's certainly no hard sell there.
The time commitment for me to post the weather forecast and arts and networking events is probably no more than five minutes daily, and I do it while drinking my first cup of coffee, which means many people who check social media early each day will see my posts. That those postings work for me is evidenced by the people who mention them to me in person or who comment on them online. A few have said they don't bother looking elsewhere for the weather, that they just appreciate the (very) general summary I provide.
I encourage you to think about your target market and the types of information that might matter to them, choose one or two info types, and start posting them regularly. You won't likely find people beating down your door to buy stuff the first days you post information, but if establishing an identity and building long term relationships with your market are important, being regular is a good way to work toward both objectives.