Feminine energy is expansive, flowing and fluctuating, whereas the masculine is central, still and consistent. For men who have masculinity at their core, living from this place is vitally important. Learning to 'be in your masculine' is what will allow you to feel that you are living true to your identity and will provide the energetic balance to your intimate relationship and even allow your children to feel secure in your presence.
More than just trying to be a certain way cognitively, taking on these energetic qualities and living from there requires accessing the masculine. If you are at your core masculine (this is irrespective of gender or sexual orientation, by the way) then you will access this primarily through your body.
Trying to 'be a man' from your head won't work. At least no real lasting effect can be created in this way. And the superficial nature of any behaviours you start to exhibit can have a negative effect as you and others (particularly an intimate partner or prospective one) sense a 'dishonesty' in your character in the moment.
A key practice in reaching and accessing the masculine then is grounding. This is done through breathing regulation and visualization which has a very real effect on the nervous system.
Below is a simple exercise for doing this. You can close your eyes or allow the eyelids to simply relax as you let your vision gently focus on one area.
1) Standing or sitting up straight in a chair, have your feet planted firmly on the floor. Gently but solidly stamp your feet a little. Become aware of their firm contact with the ground.
2) Breathe in, preferably through the nose with the mouth gently closed. Breathe down into your belly - imagine the breath travelling all the way down to below your navel. Imagine your lungs are located there, as if you are filling a balloon in your belly with your inhalation. Feel your abdomen expand.
3) Allow the air to travel back up and out, again preferably through the nose, when it feels time to do so. Don't force it. Feel the belly relax as it naturally contracts back to it's neutral position.
4) Repeat this cycle and get into a gentle, natural rhythm. When you are comfortable, start to simply observe the process as it happens almost by itself. Just notice the breath as it enters and exits the body.
5) Having got into this rhythm, now again become aware of your feet that are planted firmly on the ground. Feel them perhaps become heavy, maybe even imagine them sinking into the ground...
6) Now feel as if roots where growing our of the soles of your feet. See them reaching into the ground and becoming as one with the earth beneath you.
7) Notice that feeling of solidity. Feel your legs rooted into the ground. Now in your own time, open your eyes if they were closed or refocus them if you were staring at a single point. Feel yourself come back out of this meditative state and be back in the room, in the here and now (if you felt like you left it).
Notice how that feels. I won't bother describing it, because if you did the exercise you will know! Now imagine taking this energetic quality, this focus you have into all the various parts of your life. How much better will you perform as a man if you lived from this place?
You are now grounded and centred having accessed it through your body. You are currently 'out of your head' and living from your body , and this is central to living from your masculine.