Last weekend I got to spend some time sketching outdoors, and was again reminded of what a tough subject Australian foliage can be. The tree I was trying to draw had a particularly open leaf structure, creating a dappled effect that was a real challenge to capture with pencil, certainly given the timeframe and scale that I was working in. I plan on seeking out some Australian landscape artists to find out how they tackle this subject. I wished I'd had pastels with me, or even tinted paper and white chalk so that I had the option of adding highlights, instead of trying to reserve them. I thought about watercolor, and how I'd need a lot of gum resist to deal with the bleached white tree branches. Some subjects have a natural affinity for certain mediums. Which isn't to say you shouldn't persevere with a difficult or challenging combination! But don't let your usual habit, or the expectations of others, constrain you. When a subject offers a beautiful line, why not reach for a pen? If there's the opportunity for sparkling highlights, why not use gouache or chalk? Sometimes a friction between subject and medium enhances creativity, and sometimes a natural affinity is what you want.
Photo: Leafy lane at Yarongabilly Caves, (c) H South.
Sometimes artists use a combination of techniques in a single picture - including line, tone, expressive mark-making - to create certain effects in their drawing . With practice, different techniques become tools that you can use almost without thinking, switching from one to the other, depending on what the subject and the drawing call for. When you're starting out, or working on developing a particular technique, it is important to identify what you are trying to achieve, and know what you need to do to get that result. 
I love fantasy, action and adventure movies so I'm really looking forward to seeing 'Thor' starring the Aussie actor Chris Hemsworth (George Kirk from Star Trek). The movie is based on the Marvel comic book and I don't think spends much time in the ancient world - Thor looks like a thoroughly modern hero! Here's a more traditional comic book take on an heroic Viking character for you to draw.