Review and Analysis of Some of Last Week's Games

I won some, I lost some. It's my losses, however, that I'm most concerned with. Particurly the following two games where I failed to convert a substantial material advantage into a win. How to improve?

One of the lessons here may be that should the white opponent play b3 showing a desire to fianchetto his kingside bishop it's be a good idea, if possible to get your Queen out on f6 square threatening the rook. Also, when given a material advantage it seems like exchanging pieces is the way to go. Plus, in this case, I should have got my Queen back into battling position as soon as possible. Finally, always be careful not to allow your opponent to use any tactics like forks and pins.  

Here is the next game where I squandered a big lead and ended up losing:

Submitted without comments are two of my wins from last week, one against a much higher rated player: