One of the biggest beginners mistakes happens this way.
We're finding ourselves over stressed, maybe dealing with anxiety, and we've decided to try meditation for relaxation to reduce stress.
So you learn some simple techniques, such as deep breathing, etc, and we decide to start trying them when we feel stressed and anxious...
here's where we've gone wrong already.
When you're first learning to meditate or induce a relaxation response in your body, the hardest time to get to that state, is when you're at your most stressed. Once you've learned how to meditate, and how to enter a meditative and relaxed state through your practice... THEN apply it to reduce stress during times of high stress and anxiety.
When you are still in the learning stages, try instead to practice meditation and relaxation techniques when you are at the most relaxed time during your day/week, rather than the most stressed.
Once you are able to go from a regular state of mind to a relaxed and meditative mind state easily, then you can start to use meditation and relaxation techniques as an effective strategy to reverse stress and anxiety.
It is a bio-chemical phisiological impossibility for the body to experience the state of anxiety - flight or fight response, and be in the relaxation response or meditative state, at the same time. Once you learn how to create a relaxation response or meditative state in body and mind, you can even stop a panic attack in it's tracks.
So make the learning process faster and easier, and pick times to meditate and relax to begin with that are naturally more relaxed times for you.
Likewise, start with very comfortable positions and simple techniques. Postures for meditation that are uncomfortable to prevent sleep are great for people past that beginning stage, but may actually hinder you from entering a relaxed or meditative state if you are still learning how to get into that state.
So kick back when you're feeling pretty good and find the most comfy position you can and make your beginning steps into meditation as smooth and easy as possible.