I seem to struggle with fights late game ( probably because i forget to buff ). When is it a good time to buff and a bad time to buff in combat?
Well, here's my advice. You will notice that there are different versions of the same buff. For example, my Swashbuckler has the following agility buffs...50% for 10 rounds, 75% for 5 rounds and 100% for 3 rounds. If you're on a large battle board like the Brawlin' Hall, start with the buffs that last the most number of rounds. As the enemy draws near (or in my case, as I approach the enemy :D) use the stronger buffs that last the least of amount of rounds. The same goes with shields like Valor's Shield and Valor's Fortress. As far as buffing goes, the only bad time to buff is too early with one that only lasts a few rounds because by the time you engage the enemy, the buffs will expire. I have been in very few battles that last 10 rounds, so it's never too early to use the longer lasting, less powerful buffs.
Some will depend on who or what you're fighting, how big the battle board is, how fast your crew (and their crew) are...
Big battleboard, feel free to take a round moving forward, so when you do buff, you're not wasting a turn of that buff waiting for the next round. Use the longer lasting buffs (which tend to be weaker) first. If you're fighting creatures that use magic, get whatever will buffs you can on as many of your crew as possible to minimize the damage as much as possible. Same for any other type of attack. Protect your crew from as much damage as possible that way.
Small board, use your best buffs immediately and lay into the enemy. From MooShu on, my tendency is to buff and then focus my crew on one or two individuals at a time. My privateers hang back and keep buffing and healing (with the occasional gunnery barrage to break the monotony). My others (except witchdoctors) just jump right in after that first buff round. Witchies of either gender hang back and shout encouragement while they cast whatever spells they can think of at the enemy.