SableWyvern
Hero
The system I use is based on the Rolemaster system, where players allocate skill ranks for their next level each time they level up. For example, when reaching 3rd level, a character allocates his skills for fourth, and gains the ones he allocated when he reached 2nd.
Between levels, characters are expected to make use of/train in the skills they are advancing. This may mean simply making some use of the skills in question during normal adventuring, making use of down-time to receive instruction from other PCs, or actively seeking out instruction.
If a character hasn't received any practice with his increasing skills when he levels up, they will advance as soon as he does receive some instruction.
For new classes, I use a similar system, depending on how divergent the new class is. Simply spending time receiving instruction from and sparring with the party's fighters, as well as participating in armed combat, may be sufficient to gain the fighter class; while a PrC may require contacting an organisation, extended training or the like - dependant on the exact nature of the class.
Between levels, characters are expected to make use of/train in the skills they are advancing. This may mean simply making some use of the skills in question during normal adventuring, making use of down-time to receive instruction from other PCs, or actively seeking out instruction.
If a character hasn't received any practice with his increasing skills when he levels up, they will advance as soon as he does receive some instruction.
For new classes, I use a similar system, depending on how divergent the new class is. Simply spending time receiving instruction from and sparring with the party's fighters, as well as participating in armed combat, may be sufficient to gain the fighter class; while a PrC may require contacting an organisation, extended training or the like - dependant on the exact nature of the class.