Three pieces of advice.
(i) Have a plan whenever you make a move. What does your move threaten to do? How can you exploit the position if your opponent doesn't respond? How should he respond to avoid that? How will you respond to his response? What will you get out of the situation in the end?
Ex: you play R5. What are you threatening to do? Obviously you're threatening the black stone, but it's not a credible threat: once black adds a second stone, he's stronger, and you're weaker. (This is why we don't go all over the board playing right next to enemy stones.) Another threat is to push along the 4th line, getting influence over the entire center of the board while black is confined to the side.
If you had played R5 with this threat in mind, you would have expected B to respond with Q6 (to keep you out of the right side). When he failed to play Q6, you would have then followed through on your threat.
(ii) Follow this rule of thumb: unless the life of a group is at stake, don't play on the second line (much less the first line) until every group on the board is definitely alive.
(iii) Have you heard of tsumego? Take a look at these:
http://senseis.xmp.net/?BeginnerExercisesYou can find more other places on the internet, and in books. When the life of a group hangs in the balance, these will help you make the right move; over time, you'll be able to see what affects the life and death of a group far in advance.
