Mindful meditation is a skill that becomes easier over time. Regularly completing this will increase our ability to become mindful more often.
For beginners, it is best to use a guide to start with, such as an audio or video recording. These are easier to follow, as they have more descriptive and engaging things to focus upon. These are an effective form of mindfulness, and they are simple to practice. See below for the basic steps to start a guided mindful meditation.

First start by getting into a comfortable position. The most popular position is sitting with your legs crossed. If this is too difficult, it can also be completed by laying down or sitting on a chair as well.

During the meditation it is best to focus upon your breathing. This is an important aspect of many different meditations. Many of these guided meditations also feature breathing exercises, where a guide announces where to breathe in and out. Guided meditations sometimes use visualisations in their recordings, such beaches or forests to draw attention to. All of these inputs create a better sense of calm and mindfulness.
During the exercise, if your thoughts come up at any stage, just allow them to pass and do not place any judgement upon them. This is another skill that takes time to learn. Over time it becomes easier to complete guided meditations with fewer intrusive thoughts, and this skill becomes better in our regular lives.