I don't follow users based on their amount of Steem Power. I follow them because they are upvoting my posts or if they have good content on their blogs. It's useless to follow users who have a lot of Steem Power just for getting the possibility that they might vote on you. Usually big fish won't even notice you so don't bother. I think the best strategy to grow your account is to make friends who have a low amount of voting power. You need to keep engaged with them, motive them and then you'll grow together.
When I started out I upvoted big accounts. I hoped for some big upvotes in return but of course that did not happen. I started engaging with people who had a similar amount of Steem Power. The result was that we all grew together. To give an example, the first people I followed only had about 20 or 50 Steem Power. Now they have about 2000 or 5000.