First of all, read the tutorials and take notes you can refer to quickly.There is so much to remember you will overwhelm yourself. But rest assured if you mess up someone will let you know. Don't be afraid to try. This is a very user friendly site.
Depending on what you are writing about may influence the length of your hub. A research article or fictional story may merit more words than an opinion piece or review. Use as many text capsules as needed to make an attractive looking article. Too long a run in content without separating some of it will bore your audience. Use your own pictures when possible, but if you must use another, be sure it is public domain and you credit where credit is due. Copyright applies to pictures as well as contents so we don't want to infringe on some else's rights to ownership.
Have fun here. Make friends and comment on their hubs. They'll return the favor. Don't expect to get rich writing Hub Pages right away. Some make a good profit here while others struggle to make anything. It all depends on how much time, effort and talent you have to put into it. My main reason to be here is for the exposure and the friendly feedback. Practice helps with any craft and Hub Pages is a great platform to practice your writing. If you are an expert at anything, all the better, you'll do well here. Welcome to Hub Pages.