Direct influence is pretty weak.
You can test it, tell your members to do something. What was your conversion rate? 10%? 5%? 1%? It's usually somewhere in that region.
People don't like being told what to do. This is especially true in branded communities. They like believing they have decided to do it for themselves.
Do you know the biggest influence on community members? Other members. People do what they see people doing.
If you want people to do something in a community, you need them to see people doing it.
If people do what they see others doing, you have the chicken and the egg dilemma. How do you get people to make a desired action in the first place?
Invest time building relationships with your key 50 to 100 members of the community. You need to build and sustain these relationships. When you want something to happen in the community, you can ask this insider group for their advice and opinions.
You can incorporate those ideas into the activity (to give them a sense of ownership) and work with them to make it happen. That insider group are the people that begin taking the desired actions in the first place.
Once people see this core group of individuals taking that action, they follow suit.
You can start discussions on topics or activities you wish members to participate in. You don't need to tell people to do anything here, you need to ask for their opinions and ideas on relevant topics. Reply positively to people that suggest an idea that fits in with what you want them to do.
You can also use your sticky threads. Whenever a member mentions an activity or action that you wish to encourage, you can set the post as a sticky thread to ensure more people see that action. You may also include these as a 'what's popular?' selection on the landing page of the community.
If a member moves closer towards the activity you want, ask them what they would need from you to make it happen. Ask who else in the community might be interested in being involved? People want to hop aboard something they believe will be popular.
You can also be more responsive to positive contributions and less responsive to contributions you wish to encourage. This is the subtle act of steering the community in the direction you wish it to go.
Content is your second biggest tool of influence. You can use content to give a huge amount of attention to the topics/actions you wish people to take. Don't overplay your hand here. Don't force the agenda. Use your content to give attention to people that are already taking the desired actions. Reatively create the agenda.
You can write content which mentions them and their actions. You can interview them and let them talk about their actions. You can highlight their milestone achievements. You can create polls for people to vote on a relevant issue raised by members. You can create a member of the month award given to a member that has taken the desired action. You can include such actions in your community's history. You can give members who have take the desired actions opinion columns within the community to talk about it.
As more people begin to take the desired actions, you can develop specific events/activities for the action. You can develop a live-chat, led by members, about the action. You can help your members set up a specific day to participate in that desired action/activity. You can turn that action into a challenge for members to participate in and keep score of it.
Remember to be reactive to members taking the actions, don't try to force your agenda directly upon your members. Your members want to feel ownership of their contributions. They want to feel the community has risen up to undertake this action.
Your biggest influence over a community is your subtle influence. If you master subtle influence, the value and effectiveness of your community will increase significantly.