If you're relatively new to poker, then one thing to bear in mind is that the bluff is one of the most over-used tactics in poker, and can make for very costly mistakes.
It's less about how much you bet (you want to be enough to put someone off, but not risk more than you need to or look like it's just trying to buy the pot, but the exact amount depends on your opponents and the table conditions and what kind of hand they have and more), and much more about psychology and position.
Being in late position gives you the advantage of being able to see if someone looks weak or not (and therefore how likely they are to fold to a bet), and the psychology comes in when you're trying to work out what kind of person they have and what kind of hand they're likely to have. Some people will rarely fold, especially on the river, and you'll have a hard time bluffing them. However, others will play very tight, and will often fold when the flop misses them.
The other thing to be aware of is what the other person is likely to fear. Overcards, and cards that make a straight or flush possible, those are often cards which will either improve someone's hand or make them think about folding. Equally when the board pairs one of the lower cards, this can give a player pause for thought. It's not very helpful to think of particular cards (like Aces) as 'good for bluffing', it is far better to think in terms of likely
hands for the opponent to have and what cards would make them think that you have made a better hand.
Just don't fall into 'fancy play syndrome' and throw away money on hands where all you can do is cut your losses.