The most common and most likely answer to this crossword clue is the 4 plus 2 letter word STEP UP
I've seen this crossword clue in The Sunday Telegraph
S
T
E
P
U
P
More clues leading to the result STEP UP
- Provide more of drink, holding favourite item back
- Upset manipulated figures losing a penny increase
- Estimates from the right assuming record increase
- Progressively raise setter, regularly clipping dog
- Accelerate promotion
- Increase pace, winning
- In haste pupils advance
- Come forward with this neat clue, ultimately, by young setter
- Climb and come forward
- Volunteer set off with canine
Buddy explains!

The straight part
We know that "Come forward" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case come forward = step up.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does STEP UP mean?
STEP UP noun- (exercise) A workout movement wherein one leg stands on an elevated surface and lifts in the concentric part the rest of the body up onto it to target – depending on angle and starting distance of the other leg and weights applied by the arms – the femoral and gluteal muscles variously.
- That increases in stages.
- (of a transformer etc) That increases a voltage.