Pay attention to these tips about finishing and your results will improve.
Make sure your surfaces are scraped and sanded, especially those hard to reach areas, before gluing. This means you won't have to figure out how to get one of those triangular sanders into a place that's really tucked away. Keep all your flat surfaces really flat, particularly around joints. Use a #80 cabinet scraper or a sanding block to help with this.
There is no need to sand past 220 grit, unless you really like sanding. Then sand to your heart's content but know that you will see no appreciable difference in your finish over time sanding past 220 grit.
Check your surfaces for sanding scratches and errant little puddles of glue by wetting down the wood with a rag dampened in paint thinner or turpentine. This wets the wood long enough for you to inspect it carefully. Have the wood between you and a light source like a north facing window. In this way, the light will bounce off the wood towards your eye giving you a great view of every little imperfection. Do this for only a short while or you are guaranteed to drive yourself crazy.